There are a number of threads here about pto's cutting out, and not working the way they should. Lots of possible causes, most common is usually related to wiring, and those **** safety switches. You didn't give much info on your mower, but I doubt that the clutch is shot. My LT1050 is in it's 11th season of mowing, and has 1,055 hours on it, pto is the original one and still works fine. I have had to hunt down, and repair bad electrical connections relating to it's operation though.
Wow, I got censored....the missing word starts with d