| There were some old posts about rear control arm failures after polyurethane bushings were installed. I wanted to revisit this topic because I think I have a pretty good idea what caused those failures and how to avoid them in the future. Here is the thread in question as well as the photos, note the signs of rust in both photos. La-Z-Link 
My theory is that these failures were caused by rust due to trapped moisture between bushing and arm. In both failures, there is a particular Energy Suspension brand one-piece poly bushing with no outer metal sleeve being used. This is significant because OEM suspension arms are stamped steel but coated/painted from the factory. When an OEM bushing and sleeve is pressed out, it takes some of the paint with it on the inside of the arm, leaving the raw steel. If another bushing with a metal sleeve was to be pressed in, it would not be a problem as the compression of the sleeve against the steel of the arm is basically air tight. If a poly bushing WITHOUT metal sleeve is installed, there could be a risk of moisture being trapped between the bushing material and raw steel of the control arm. In the photos of the failures, the are indications of rust which supports my theory. This is not a problem on the aluminum knuckle side, and also not a problem if the poly bushing calls for the OEM sleeve to be retained. For example, Energy Suspension’s poly bushing kit for the Z’s front lower control arms call for the sleeve to be retained, which is why people drill or burn out the old bushing material instead of pressing out the entire bushing/sleeve together. With these rear control arms, the poly bushings call for the OEM sleeves to be pressed out before install. As you can see below on my NA toe arms, pressing out the OEM bushings with sleeves left the steel unprotected. 
The solution here is to grease the inner diameter surfaces of the control arm socket to protect against any rust and also cut down on noise. Here is the problem though, due to the ES bushing being a “one-piece” design, it has to be pressed in like a normal bushing would. Since there isn't an outer metal sleeve on these ES poly bushings, a powerful press isn’t required and you can use a simple bolt/nuts/washers rig to press them in. This is a huge pain though, because one side of the poly bushing always wants to slip in and not seat into the arm equally. You have to do weird stuff like use a worm gear clamp to try and keep equal pressure around the bushing as you press it in so it actually seats in equally. 
*******THIS is the issue******* Regardless of whatever method you use to press the bushing in, the bushing is always under tension scraping against the sides of the control arm as it is being pressed into position. Whatever grease you might apply to the bushing or the socket of the control arm is just scraped off as the bushing is pressed into place. So it is basically impossible to get a proper application of grease between the exterior of poly bushing and the raw steel surface of the control arms when these particular parts are installed. After enough time and trapped moisture in the right climate, the arms rust out and fail. Enter the Whiteline two-piece polyurethane bushing design. ES on left, Whiteline on right: 
Since this design is in two pieces, they can easily be inserted by hand into the control arm. This lets you grease the crap out of the unprotected steel. Below you can see one side of the white line bushing inserted. There is no way you could ever get this same amount of grease here with the Energy Suspension single-piece design and the way it has to be pressed in under tension. 
Another good comparison of the two different bushing designs is the rear lower control arm bushings from both Whiteline and ES. The whiteline versions are the more traditional variety that have exterior metal sleeves. The exterior sleeve and control arm socket would not be greased on install. 
The Energy Suspension version do not have the exterior sleeve. I could only find a photo of a large kit, but you get the idea. These are the same "sleeveless" design bushings that failed in the photos and still on sale. These WOULD need to have grease applied to the exterior on install, but like I pointed out above, it is not possible to get a good application of grease in there due to having to press them in.
 I just want to be clear that I am in no way saying Energy Suspension is a bad company and these not even a bad product, I run both Whiteline and Energy Suspension bushings on my car and equally happy with both. It is just these particular ES products are not a good design for the z32 rear arms. So these are the big cliff notes and takeaways here: If your polyurethane bushing does not have an outer metal sleeve, you must be sure to grease the outer diameter surface of the bushing and inner diameter surface of the control arm bushing socket. I think anyone running this single piece ES bushing in any rear control arms should inspect for rust and consider swapping out for the whiteline products. One more thing I wanted to cover was proper greasing of polyurethane bushings regardless of design or brand. If I’ve understood this correctly, the metal bolt sleeve installed inside the poly bushing is held totally rigid when the arm is torqued to the car. As the suspension moves, the poly bushing is moving around that inner bolt sleeve, and that is the surface where it is most important to keep greased. In the below photo you can see I have the Whiteline rear lower control arm bushings installed, same ones that were pictured above. You can see there are little diamond channels cut out on this inner surface of the bushing to hold as much grease in that location as possible. So when you go to perform regular maintenance greasing on your polyeurthane bushings, you actually need to pull out the bolt sleeve and grease up the outer surface, as well as inner surface of bushing, before reinserting the bolt sleeve. 
Here it is fully greased up and ready for the sleeve. 
Yes lots of grease there, but not worth cleaning up until the part is installed. There should be NO NOISE with Poly bushings installed. If you have any noise, something is not lubricated properly. Overall I’ve appreciated having the poly bushings installed in the rear end suspension. The whole rear end feels tighter, particularly when pushing the car a bit. I have noticed a slightly more rigid ride, but I was able to dial it out easily by softening up the rear adjustable KYB shocks.
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Revisiting rear control arm failures with poly bushings - 
