The bushings are in the shift control rod, which, I noticed, has also been discontinued. They used to be serviceable on older models, but it looks like they are part of the rod assembly going by the part diagram (see link below). There is a spring in the diagram, part # 34573-4M500 (part code "34573" in the diagram), but it's impossible for me to say if that is your problem or not. You also have a socket assembly (part code "34553") with a bearing, spring and seat which could fail that can cause issues like yours. If you don't feel confident with the shop you took it to originally, you could always get a second opinion. If you can get the car to where you can get under, you could check to see if there is any noticeable play in those parts. Unfortunately, I can't really tell you much more without be able to check it for myself.
https://www.nissanpartsdeal.com/part...(2=QG18DE;5=MT)