The R4 can work fine. I have one on my 1984 300D and a Sanden (w/ RollGuy's brackets) on my 1985. Both cool the same, as best I can tell. I had little faith in the R4 since uncharged when I bought the car, but I charged w/ Duracool and works fine w/ no leaks. If it fails, I have a new R4 I got cheap on ebay (listed for GM, looks same). Your question perked me to go look and it does have recessed ports like your new one.

I imagine GM owners deal w/ the same issue, and it looks like a tractable problem. Perhaps put an O-ring around each seal to keep it centered. On the Sanden, I put a rear head w/ "GM Pad" to use my factory hoses. It has O-ring grooves. I prefer that to the special R4 washer-like seals.

I use PAO 68 oil, which is supposed to stay in the compressor better, which an R4 should appreciate (no sump). It is compatible w/ all refrigerants and doesn't absorb moisture like PAG. You could break the fitting on the suction tube near the compressor and pour the oil down that. You should replace that O-ring anyway.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans