Toro Z 5000 rear wheel locking up

all of the sudden after stopping momentarly the right rear wheel locked up I was able to twist it by hand to get it loosened up but it happned again several times feels like something mechanical
& the dealer wants to charge me 60.00 an hour just to diagnose & wouldn't even guess how long it would take I get the feeling they would just like to sell me a new mower & I am getting the feeling they just lost a customer
Any Ideas ???
JJ

Is this one an old timer ?
I do see tens of hours and major transmission work, as a guess...

How did you make out? I'm thinking wheel motor and possibly a pump.