The FD has a pretty good size leak where the high pressure line comes out of the compressor. I've made sure that the fitting is tight, but I'm not really sure what else to do. The system was converted to R-134 before I bought it. Does compressor oil fix something like this, or do I need new lines/fittings at the leak? If I can get replacement parts from someone tearing out their AC, is reverting back to R-12 out of the question? What might I need for that? I'm not too familiar with FD systems or AC in general, and I'd really like to have an unadulterated AC with that nice, cold R-12. (I'm sitting on a few tanks of R-12 that I've been keeping incase the FC needs a recharge one day.)

Any advice is much appreciated!

 

There should be and o-ring on that fitting. I would start by draining the system and replacing the o-ring. Then see if it holds a vac. before you recharge it.