Use new steel shim in back. Obtain some seal that is specifically designed to seal pressure barriers. I got some special stuff from a local AC guy but cannot remember the actual name. Make sure you spend the time on that suction seal. Mine leaked down with R12. expensive mistake.

Discharge uses an o-ring only.

I pressured the system to 125 psi and made sure it held. I used Joy dish soap and water mixture to check for leaks. A/C guy advised 'Joy' because it makes the best bubbles. Left if for 5 of 6 days to make sure.

Also, Make sure your EPR valve (inside the suction hole) is functional. Both my AC cars needed to have it replaced (Evaporative Pressure Regulator). I have heard the system can work without it. From what I understand its function is to keep the evaporator from freezing up. All I know is that with a non working example in my RV2 pump, my A/C would not get cold.