On my Ford 2120 I never have used the PTO a lot but it has always worked when I needed it for the last 20 years. For some reason this year while pulling the spreader it would not stay engaged. Kept popping out of gear. Had to eventually get another tractor to finish the job. The only thing I can think of was the hydraulic fluid and filter were changed and this is the first time I have needed to use the PTO since that. Some one had suggested maybe some dirt got in there, not allowing some of the check balls to seat properly (this is where I start to get lost). Talked to the shop and they start talking about "splitting" the tractor which makes me shudder at the cost involved especially if there is an obvious quick fix I could do at home. Any ideas?