I quit posting about the A/C saga on my Newport because it was just getting fucking ridiculous, but I finally got it sorted. Spent probably 10 hours collectively swapping seals, trying different installation methods, etc. Carbon seals are so damn finicky. Went through two reproduction santech seals that were crap and didn't work.
I finally ended up making one good seal from two old seals. Took the good rubber piece from my original compressor, and the good carbon piece from the compressor my buddy gave me. Soaked them in oil for two days. Meticulously cleaned the sealing surfaces of the carbon and installed the front cover, turning the bolts 1/2 turn at a time so it seated perfectly flat. Held vacuum and pressure immediately. Charged it with propane. Blowing icy cold now. Probably not even going to bother ordering the Frosty Cool 12a honestly, it's working really well and I don't feel like discharging it and risking losing the seal again. Probably won't happen, but still.
I was just about ready to say fuck it and convert to a sanden compressor, but I really didn't feel like spending $700+ for that. If this seal fucks up, I feel confident that an NOS seal from eBay will work. Even if they are $80, it's better than converting.
I was basically battling Chinese manufacturing standards on a very low tolerance finicky part. A tale as old as time.