The return line from the compressor carried oil back to the pan after we punched a hole in the side and threaded it with a 3/8-NPT-pipe-thread tap. This part was a little scary, but after hitting the oil pan a couple of times with a big hammer and a punch, the experience became cathartic. We thought we had a 3/8 tap in the ol’ tap and die set, but guess what? We didn’t. NPT stands for National Pipe Thread, not the same as the stuff in a standard set. Obvious to some, but not to us at the time. The result was a two-day delay because all the oddball-tool stores had closed by the time we learned the score. With the hole tapped, we screwed in the return-line fitting and attached the return hose. No leaks yet.