I have a friend who just purchased a 9650STS this year and while doing corn was rained out. Got back in it after a few days in the shed and it would not back up in 2 wheel but in 4 wheel, it would . Had dealer out, diagnosed bad hyro, Installed motor an pump,SAME thing. Reman unit must be bad, Replace and same thing. Dealer and mechanic stumped. Any ideas as to what could be happening??? He took off to finsh corn in 4 whl drive but would like to fix it.