MyRB67 Pro shutter button is sticking a bit. I've turned and unturned the knurled washer a couple times, and it still sticks unpredictably with both my lenses. Whats up? I've checked all the safeties and I think they are OK. I can never be sure if its going to trip when I want it to. Sometimes it goes if I push it a little harder with my finger, and sometimes it doesn't. With a shutter release (which I always use when taking pics), I won't even try to push it harder if it sticks.