The reman 4 Seasons heavy R4 that I bought had o-rings. Do not remove the plate until you are ready to charge the system, it provides a pressurized seal. Under the plate should be o-rings. You can re-use them (the ones on mine were black) or replace them with better HNBR o-rings (what I did).

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked