I put the electronics back onto the original chassis and i think you may be onto something, the servo stopped acting up unless you touch it in a very specific way.

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It baffles me, it looks to have something to do with vibrations, but it seems to do it more eagerly when i touch the servo and topdeck both instead of just the servo.
The mystery is solved though, i'll pull the servo apart to see if anything obvious is loose or broken, but i'm afraid it'll come down to a new one..

Edit : a cable was pinched inside the housing against a sharp soldering, rerouted it to the other side of the servo and all seems good for now.
Also really strange as this servo was advertised as having the cabling on the inner side, however the housing does not have the notching on the correct side to allow this, It seems to be pinched by default.