Everyone looks at the situation differently. To me, putting 1/3 more $ into a $300 rifle is not the way to go yet. There are literally thousands of Lyman GPR flinters being used today using original locks with no major problems. No, it is not a $ 100. lock & it will never be. But it can be fully functional & still work fine. I have had no major problems with mine, it is all original, it has about 5000 shots thru it and lots of people do the same.
Do the vent mods & try it, it usually cures the problem. That and a lil practice with it & learning what makes that particular lock work best. Usually 1/2 pan of powder, freshly knapped flint, don't have Any powder laying in the vent hole, wipe the Frizzen clean first, then the pan, thenflint & Under the flint after Every shot, etc. You will find this will make a difference. When you carry the rifle when hunting, carry it with the lock tilted out so the pan settles Away from the vent hole, not in it.
I would not do a Chambers vent liner change until you really know flinters, (an possibly never on the GPR as mine didn't need it) as you will be pulling that vent liner lots of times while you learn. The Chambers vent liner is top of the line (IMHO) but it is non-removable, so delay that a bit.