I used to have the same problem with my BX22, and I found that a small ball pean hammer tapping it off was the best way. I would drop the mower deck out from under the tractor and then only half of the driveshaft was much more manageable. I finally got tired of dealing with it, so I got under the tractor and using a can of spray brake cleaner and a brass wire brush, I cleaned the splines til I got every bit of grime off of it. Then I did the same with the driveshaft coupling. I started by putting the part that you pull back into a coffee can filled with carburetor cleaner and left it to soak for a day, then I started cleaning it with Q tips, a dentile pick, and rags. Once it was as clean as it could be I sprayed it with a light machine oil to keep it from rusting. Never had another problem with that mower deck coupling. When there was nothing on the PTO shaft, I would put a tight-fitting plastic sleeve on it to keep it from dirt accumulation.