The monovalve is not a perfect seal. It won't leak so much that it hurts the cooling performance to any really noticeable degree. The silver temperature regulator box behind the glove box tends to have capacitors that leaks out electrolyte and cause all sorts of crazy temperature regulation issues as well, sometimes running the heat in any position of the temperature wheel except min cold.

I've seen systems grossly overcharged (my SDL was way overcharged from not paying attention once) running head pressures up to 400PSI and tripping the overpressure switch and they came around just fine once the charge was corrected. If you didn't blow any seals or hoses, you're probably fine.

I still say you're just grossly overcharged.

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Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]