Also possible that the mainspring is getting weak. I'm not sure whether or not the Tingle had a coil or leaf spring (probably leaf, not many custom builders used coil springs) so that's something to consider. As MD suggests, try a new nipple first (make sure you use the proper threaded nipple) and make sure there's nothing rubbing or binding inside the lock. Lock screw(s) that are over tightened can cause this. If the problem persists there are some good folks out there who can tune and/or replace lock parts. Dixon Muzzleloading and Track of the Wolf are a few to consider.

BPS