symptom: cruise won't hold a speed, let's go

The cruise amp in my 87 300D had been replaced by PO with a newer one, date code 2.02. Done at dealer.
And from service records see that a "redundant ground" pin was pulled from the harness plug, so it's missing a tooth. And that tooth is just dangling in air behind the plug. Hmm..

Anyway...

I had a 1986 cruise amp on hand from a parts car, so I put that in and I also put the dangling pin back into the harness plug so all 14 pins make contact. Cruise works again in my car.

Anybody know anything about pulling this pin to make the replacement part work (better) in the 87 300D.
The markings on the newer VDO amp are:
2.02
12V
412 212/001/007
Mercedes Benz
023 545 21 32
ink stamping: 198 2.02

And this newer amp has what looks like a personality plug on the back, probably containing resistors... it's markings are:
(benz logo) 12 01
005 545 46 32
VDO 519201/1/09
Made in Germany

I plan on re-soldering the newer amp and putting it back in to replace the old one again.

Just curious about this pin modification on harness for it, obviously sanctioned by MB.

__________________
Cheers!
Scott McPhee

1987 300D