You're still focusing on the wrong things. The vac amplifier is not going to follow the VCV. The vacuum modulation on the turbocharged OM603 is a radical departure from the crude system of switches used on the 617 and 616. What you are expecting and what really happens aren't the same thing. The vacuum sent to the modulator is biased by boost. If you aren't building boost, the vacuum will still be high despite the VCV bleeding off. You need to make sure that all of your inputs to the vacuum amplifier are correct before proceeding further. Don't use brake cleaner, you'll ruin the rubber diaphragm in the amplifier.

Erratic shifting sounds more like transmission problems (wear), misadjusted bowden cable, or broken springs in the accumulator springs positions.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

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