If you have a Nippon compressor check this place for parts:

http://www.acsource.com/cgi-bin/SoftCart.exe/scstore/denso_c.html?E+scstore

and look here for instructions:

http://www.pelicanparts.com/techarticles/911_Nippondenso_rebuild/911_Nippondenso_rebuild.htm

Before spending a lot on parts to fix a leak, you might try a leak sealer like Super Seal Pro. I used it on an '81 Eldorado and it held a charge for over 2 months before I sold it.