Maybe I just got a bum lock, I don't very often use L&R locks so that could be the case. They do now use a forged mainspring instead of the cast ones they used to use. I understand that casting flaws from the casting factory made it near impossible to get a mainspring that wouldn't fail after some use. The forged main spring seems to work well, but I'm not sure it would change out to replace an old cast spring with out a little wood removal in your lock inlet. Maybe it would, you'd have to try it and see I guess, wouldn't take much to fit it.
I had a fowling gun that I used their Queen Anne lock on. It was a champ of a lock, fast and dependable and I got 140 shots out of a flint once. Only problem was a broke frizzen spring that they replaced for free. Also, they replaced my worn frizzen for free at that time too. I kept the worn one on the gun and kept the new replacement in case the worn one quit working. Probably had around 8,000 rounds out of that gun or more. Used it for skeet and sporting clays.