I understand that the purpose of the hole is to get the steering centered. There is a rod tool one can insert to lock the box there (not req.). Then when you adjust the steering links on L & R (per an alignment machine) you should wind up w/ the wheel centered when driving down the road. I have never done that. I just try to get the links showing the same # threads on each side, at proper toe-in. Then, drive a bit and if the steering wheel is not centered, adjust accordingly. I generally have to tweak the toe-in after driving anyway as things settle so usually no extra work to get the wheel straight. Anyway, the only way this would affect your issue is because the box is tighter at the center, so if that point shifted to the left you might feel more binding as it sweeps thru the actual box center there. Would also mean you have the sector shaft adjustment too tight (bolt w/ locknut on top).

I expect the Pitman arm splines are keyed, as they are on my Chrysler boxes. If so, it only goes on one way so don't try to clock it per post #2. The other thing that could translate from Chrysler boxes (don't know GM & Ford) is that those have a spool valve adjustment. You loosen 2 bolts and tap the valve housing back & forth until centered so the front wheels don't self-steer (engine running, wheels off ground). I expect M-B uses a similar spool valve which has an adjustment but never been there with my 300D's.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans