Over the past 6 months, i've noticed that a few liner locking knife i own becomes extremely gritty when i keep opening and closing it. This problem is true for Spyderco Military, Buck Vantage, and even Spyderco Superleaf. For the last 2, i disassembled and cleaned up everything and they are back to normal. For the Military, i simply stop touching it for a day and it's smooth again. Anyone know why this happens?