I recently "fixed" a Colt OP by placing a coil auxiliary spring behind the rear of the bolt to keep the bolt engaged with the rebound lever. The bolt spring (part of the bolt) was weak and kept slipping off the lever cam. IMHO, the bolt is the trickiest part. The spring part is thin and can break or weaken over time, and the part can't be welded because the spring will be made useless. And it is the hardest part to obtain because so many were replaced that spare parts are very scarce. Maybe someone is making repros; if so, I am pretty sure they would require a lot of fitting.