Went out to plow last night and the unit was in 2wd. Flipped the switch to 4 wheel drive and nothing. Moved forward nothing. Plowed the drive no problem in 2 wheel drive but never could get 4wd to engage. I have never engaged the 4wheel drive switch while the unit is moving as I have heard that can destroy the front diff. A couple weeks earlier I had it on the hunting property and there were no problems or no sign of a problem. I thought maybe a fuse but there isn't one specificaly for the 4x4 function and all other functions seem to working just fine. I'm guessing a bad actuator but??? How difficult is that to replace? Expensive? Any other ideas?