Just have the shop do a full overhaul on it. Once that's done, it should work for you without problems for many years. Since 2005, I've owned nine F4 bodies. One of them was a dud when I received it. I expected that, since I'd bought it as a parts camera. Shutter had finger damage, which killed it. Every other F4 has functioned fine for me, but, sometimes had LCD bleed problems. One needed a new viewfinder, since half of the lower LCD was black, due to massive bleeding, and the hot shoe didn't work. After viewfinder replacement, it was fine.

With respect to second hand "pro" bodies being more problematic, I've found that to be untrue, since I've had more problems with well-used amateur bodies. I've had three F3's with issues (one of which I currently own), one was bought knowing the issues and was a project camera. I've had at least four FM2n's that had meter problems and two with winding/shutter problems. One FE2 with a maladjusted meter that was jammed when I got it, somehow I unjammed it and got it working again. A bunch of Nikkormats with issues, some repaired, some turned into parts cameras for the other cameras. Four FM's that had issues with various parts. I also had an F2 that began firing when I used the DOF preview button, and a couple or three F's that, due to age, had slow shutter speed problems. A couple bodies were in decent cosmetic condition, just weren't working right.

-J