Broke it.
Fixed it.
Started out this morning to do a couple of minor things. For/Rev pedals were really sloppy. Figured it my be hydraulics not warmed up, but it didn't get better. Then it quit. No motion. I'm at the bottom of my hill, on wet ground, with only a few hand tools. Quick check showed me the pedals weren't moving the HST linkage at all. Noticed a roll pin that had mostly backed out. If it had fallen out completely, I wouldn't have known what to look for. Couldn't get it driven back in ... no hammer or punch and the MMM was in the way. Was able to get it out and found a nail that would go in for a temporary pin. That was close enough to get some movement, but not close enough to really work. In superslow creeper mode ( 10 minutes for 500' !!! ), I was able to get it back up top the paved driveway to dig deeper.
Dropped the MMM off and took the pedal assembly off so I could drive the pin back in and rig up a keeper wire.
Seems to be OK now and gained some of my forward speed back, so this may have been working loose for a while.