Its interesting that this mount issue wasn't picked up during trials, after all you only have to examine the mounting system to see the rather obvious weak points.
I suppose in its defense, you could say they certainly weren't intended to, or envisaged to still be in use 45 years on with civilian shooters!
Back in the early 1970's, the L1 was due for replacement by the early 1980's, so perhaps no one considered REME Armourers would be repairing the mounts 20 years after the SUIT entered service.
I've got a few mounts and SUIT's, the best one is an earlier L2A1, that one groups very well indeed.
I must admit, I never separate the sights and mounts, I don't know if that makes a difference to be honest, but I always think best left well alone.