“…. The only way I see to fix this is to play with the two rubber bushings, in theory the front one should be 2 mm thinner and the back one 2 mm thicker.
I have no idea how to modify them, and this is assuming the misalignment is the culprit….”

It’s been many years since I replaced the rubber bushings on our old 740. However, I do recall that some of the bushings are installed in the bracket from the aft side and some installed from the forward side. Since there is a shoulder on one end of each bushing, inserting them from the wrong direction can move the accessory fore or aft or by about 1/8”.