Before you add ANY type of stop leak go to ackits.com and read up on them... Most if not all stop leaks destroy your system.. If you did a vaccum and it pulled down to 28 (which is almost perfect for no leaks) and the next day it would not blow cold or the compressor would not come on you've blown a seal by overfilling the system.. Using 134 requires less than R12. I'd use dye (kits are cheap and sold at ackits.com and ebay) find the blown seal fix then vaccum and recharge your system.
