My JD 4200 hydrostatic drive rear wheels came to a complete stop while I was driving to my shop after mowing the lawn. The steering and 3 point hitch work and when I put the transmission into neutral the tractor will roll freely. When in gear the rear wheels are locked and depressing either forward or back petals the trany makes noise but fails to move. The dealer is suggesting to take apart to see whats wrong will be 16 hours at $110 per hour. They think total bill will be between $6000 an $10000 depending on what is wrong. What to do?