I had a leaking sprocket oil seal which caused the same symtoms as you described - small amount of clean oil dripping on the garage floor after a ride but not a continuous drip, oil drips from filter after running down from the sprocket area. The leak got worse over time and was actually blowing up on my saddle bags and all over the exhaust. My dealer fixed it under warranty and said that the new seals that they were getting from Triumph were of a different improved design.
