try a new gaslock?
Are you saying that when you rotate the gas lock it rotates past the 6.00 position before getting tight ? If so it can be easily fixed with shims or by removing and reversing it so it screws on from the other side.
If you havn,t removed your flashider yet you can cut the shim and slide it over the barrel if you have to.
pm me, I may be able to locate mine..it's surplus to my needs now.