I have a Tough Torque transaxle in a JD L110 I bought 15 (at least) years ago, was my primary riding mower for awhile and now is my "Gator". I was abusing it one day and broke it. I removed it, opened it, found the gear I tore up, contacted Tough Torque. They supplied me with the replacement part, explained that mine was the low end and for one thing had conventional 10-30 whereas their higher priced units used 10-30 synthetic and all. Soo mine got syn. too on the refill. Couldn't ask for a nicer bunch of people to work with you in solving a problem.....got a free Gimmie cap with my parts too. Wow. Used to have to buy a new truck or tractor to get one of those and sometimes (1998 Dodge) had to ask for it. I think the salesman bought it out of his pocket.
Recently I put an 18hp BS V twin on the 110. In doing so, I put in new belts and checked the pulleys and all. Since I was going through everything I thought I'd check the transaxle and see how things were looking. I opened it and had another look around. Thought I'd check the TT www site and see if anything new was happening. They have upped their oil requirements to 10-40 full syn. So off to the store for some of that. Going to bet you that a lot of the problems they may have been having with their low end units were a result of oil breakdown under high stresses.