About 2 months ago I noticed the crankshaft pulley was wobbling and found that the bolt was just barely finger tight. I tightened it down to 120ft-lb and everything seemed fine until about 2 weeks ago when the timing belt jumped several teeth on just the right (passenger) side. When I removed the pulley I found that the keyway on the pulley was worn (about 1 key worth) but otherwise it looked ok. I needed to get the car back on the road so I filled the gouge in the keyway, re-installed the timing belt, and pully using blue loctite on the bolt threads and the inside of the pulley where it contacts the crankshaft. At this point the engine seemed to be running great but I was getting the occasional P0325 (knock sensor) CEL. That made me nervous so I ordered a new pulley and key which I'll be swapping in tomorrow (if I can get my loctited pulley off).
Any thoughts on what caused the timing belt to jump? The belt is only about a year (15000mi) old, didn't show any problems, and the tensioner seemed fine (required plenty of force to compress). I just don't see how that gouge in the pulley keyway could have caused the belt to jump like that once the pulley bolt was tightened but I also don't see anything else wrong.
Added: BTW this is a 97 Impreza OBS with 139,000mi