I will be maintaing the Tuff Torque K66 to the hilt........ I'm thinking of doing a change out of the trans fluid probably once a year. I'll still work it fairly hard I think. I see on the Tuff Torque site the K66 is near the top in residential mowers. So I know it is not super heavy duty.
Funny thing is I have been mowing about 1.5 acres of lawn that is fairly hilly in some areas. This using a cheap old school 2004 year Ryobi/MTD. Single cylinder Briggs Intek. Bought it used in 2017. Pulled the Transaxle apart to clean and grease it. Fixed head gasket. Ran fairly well for 3 years. Then went down a hill one day and heard a clanky sound. Time to pull apart and found compression release had been apart for some time, and got caught between connecting rod and case.
The cheap little MTD got me from a walk behind self propelled mower 8hrs ish, to about 2.5-3 hrs on the MTD. Bought the MTD for $200 and put work/parts into it to keep it working
Bought a new motor and have been mowing with new engine for 3 years. Just adjusted lash on valves and it is running well. We had 2 large maples, and a cedar tree cut down in 2016. I used the MTD with a trailer, sometimes piece of plywood I pulled to haul tree rounds to different areas of the yard. I'm pretty impressed because a lot of that wood was in hilly areas, or had to be pulled thru hilly areas.
The original trans let loose of one of the axles a couple months back. I put on another used trans I had pulled apart and lubed up to replace it. Been working well for the last couple of months. I was going to sell it to simplify, but I might be tearing apart the Husqvarna to reinforce the frame at some point. So I might need a spare to mow while the Husqvarna is apart.
Then again collecting project tractors seems to be an addiction that is acceptable in this forum.........