My Comp-Tac
MTAC leather backed Kydex front shell has been worn for pretty close to 3 years, almost, daily now. When purchased I put a drop of blue LocTite on the bench and used a modeling brush to put a very thin layer on each of the 4 fine thread screws. I set my preferred retention at this time and marked the screwhead position to the Kydex. In 3 years the screws haven't moved. The double layered leather backing has formed slightly but the set retention remains the same to this day.
Something to remember. Leather backed with Kydex shells do NOT require a super tight retention by themselves since they are designed to also use the belts retention as well. For example.. If I hold my MTAC with my Classic Walther PPQ (cleared and unloaded) upside down the PPQ will NOT fall out. If I give it a light shake it still doesn't fall out either. However, if I give it a slightly stronger shake (think shaking a ketchup bottle a bit due to the running separated liquid on top) the PPQ WILL in fact drop out. Once it is secured in my pants with the belt I can literally do flips on the trampoline and cartwheels on the lawn and it'll NOT fall out.
When I insert my PPQ into the MTAC there is just the slightest click of the detent in the Kydex slipping over the guard. I feel it more then hear it.