Had a similar issue with an 833; I don't recall the model year for certain but it was likely a '69.
The combs inside the side cover are pretty tight to each other.
What I did was loosen the side cover (in the car), tap the side cover upwards, and re-tighten the bolts.
Double-checked the neutral alignment with a 1/4" dowel (it was fine).
Problem went away.
IIRC, one of the side cover bolts is shouldered, presumably to locate the cover, but it wasn't an issue in my case (no pun intended).