I could be Warped pto clutch plates, It could just be a bad brake, lever stuck/valve is the first issue to address but if that's all needing done it's one in 100, If you've got to split it, with the fix/check it while you are in the area that a good tech will do, you could spend a lot, $20,000? A fix whats broken ,DIY, Much less, not necessarily better.