Yes, adjust the VCV with the engine off.

There are tons of 80s MB's driving around with the original VCV working fine. Hook it up and see if it works. If it's stuck closed, you'll still have excessively firm shifts. If it's stuck open, you'll turn it into a slush box. That's your test really.

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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]