I had a similar issue with my Sears "Best" 7HP/19" Rototiller. The transmission is a piece of *** in these units.
The first one broke within an hour of owning it. Figuring I got a lemon I told the responding technician to just swap with with a new one. Well, that didn't last all that much longer either; just longer than the warranty.
The responding tech for the second unit told me that to fix it would cost more than the price of a new unit. WTH...Thankfully he waived the $100 service call for me.
"Wiser but still, you know what I mean" in SoCal.
Reason of review: Bad quality.
Monetary Loss: $750.
Preferred solution: Just fix it at a fair price..