If you go that route I would keep in local (no ebay or Amazon, etc) so if issues you don't have to deal with ship hassle and easy core return. Look for good return warranty. Are you doing the replace or a shop doing it?
If you old unit uses R12 it is like gold, so do the R134A conversion since the replacement compressors are R134A units.
Where is it leaking?
FWIW the Feds are phasing out R134A so it will get more expensive like R12 did and eventually hard to get if at all. Might want to Stock up on R134A recharge cans.