A small wad of cotton or cigarette filter placed into the rubber elbow connecting the intake manifold to the transmission vacuum line will indicate if you have a leaky shift modulator. It will turn red. Probably don't want to leave it there for longer than needed to test that.

Sometimes some upper cylinder lube will free sticky rings and restore the seal. Worth a shot before you tear the engine apart.

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-tp


1990 300SE "Corinne"- 145k daily driver - street modified differential - PARTING OUT OR SELLING SOON - PORTLAND OR. AREA - PM ME FOR DETAILS
1988 560SEL "Gunther"- 190K passes anything except a gas station
1997 S420 - 265k just bought it with a rebuilt trans. Lovely condition