vstech is correct, and your gauge readings confirm it.

Unfortunately, the most common leak site is the shaft seal on the compressor. The R4's do that. Fairly easy to do (Autozone tool loan program), but requires recovering the refrigerant. Use the new double lip seal if it is the shaft seal.

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The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)