I don't understand the pessimism. A few years ago I acquired a long-action BLR for cheap, and quickly discovered it had 2 teeth stripped off the big pinion gear. Seems the previous owner was big on neck sizing only, and was happy to squeeeeze that lever really hard to make them chamber.
Anyway, I ordered in a new gear from somewhere in the US, and installed it myself. I looked at the relationship of the gears when I took it apart, and remember I used something as a witness mark to know precisely where the teeth engaged each other. I put it together once, and noted the bolt was a few mm short of lock up. I took it apart again, advanced the gear by 2 teeth, reinstalled, and all was good. It was not the nightmare people make it out to be, and I would not hesitate to do it again.