Nothing particular was wrong with it, other than it was spending more time down than mowing. I got tired off messing with it, so I found a Snapper Hydro to replace it. Basically the exact same mower, lots of interchangable parts, but with a heavy duty Eaton hydro axle and 23x10.50x12 rear tires. I have since also retired the Hydro from mowing duty, but now I use it as a garden tractor and small dozer when the tractor is too big for a particular job.
I ended up pulling the engine and deck from the LT16 and built an offset mower to pull behind the lawn tractor. As it turns out, all the problems I was having with the LT16 was in the wiring. When it was still on the tractor, that engine would run fine, then die and not restart for hours. But when I built a new wiring harness for the offset mower, it has run perfectly for three years now.
If you want the rear axle from the LT16, I'm certain it has the same dual range 6-speed disk drive your YT16 has, you can have it. I will admit one thing, I inadvertantly pulled the wrong bolt from it and heard something drop inside the case. It's locked up now, but was near perfect prior to that with no noises whatsoever. It is HEAVY, so shipping would be pricey, but give me a yell sometime if you decide you need it.