I have been through a few R4s new and rebuilt. The new ones come with those leak prone suction side GM seal washers for the ports, The rebuilds have the o-rings. My new ackits $300 GM seal R4 locked up after a year and leaked (R12)! I now have the $154 Behr (o-ring) rebuild form
www.europartsdirect.com. So far So good! No leaks! Keeping my fingers crossed! The quality of the Behr seems better than the Apco Air, Champion, Four Seansons and others R4 rebuilds I have had. To aide in compressor life I used BVA 4 napthetic mineral oil 300 visc. Good luck.