I'd agree that this is a classic low charge due to a leak (a modification of the old story of "charge in the fall, springtime won't cool at all").

Leak test while there's some refrigerant still there, fix leak, recharge. A6 series compressors are often checked by the pros for shaft seal leaks. FWIW

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The Golden Rule

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