I recently had a very similar experience with my Model S, although it was a month as opposed to multiple months that the author faced. I had a front bumper issue, and by all accounts it was a minor collision (car was moving at around 4mph). Needed the bumper replaced, along with parts that sit behind the bumper. Tesla handed it over to a body-shop who (a) sat on it due to needed parts, authorized by Tesla, (b) took time to repair/assemble as only certified (by Tesla) technicians can work on the car, (c) the certification is apparently expensive and time-consuming so most body shops can only afford to have one technician at best to be certified, (d) this leads to large delays

I can't think of an easy solution here -- as an owner I'd like the car back in a shape that's as good as before, and certified by the maker. But the bottlenecks here seem to be with Tesla.