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The stuck portion could be owing to grit shaken loose by the repair, or jarred loose by the lens (or the lens and the camera) being dropped at any time.
Or it could be owing to your having used the camera in a gritty or sandy area:
How old is the camera? in months or years since you bought it.
Has the camera been dropped or otherwise subjected to mechanical shock(s) in its lifetime?
Has the camera been operated in or subjected to, temperatures below 32 degrees F (freezing point) or above about 100 degrees F ?
Has it ever been subjected to a humidity higher than 85 % or gotten wet ?
Has the camera been operated in a gritty or sandy environment, such as a beach, a seaside, a construction site, or the like?
The repair on an 8 year old lens is a delicate one. You could try it, but being such fine work and such fine machining etc., it would be risky, unless you went slowly and carefully, and observed anti-static precautions at all times when handling either the opened lens and the electronics you are replacing and the replacement electronics you are putting in. And also, you would need to do the work in a clean area - no pets, no pet dander, no dust, etc. etc. And not touch the lenses, at all, of course.