I had this weird popping noise under heavy load, but only when turning one direction. Figured it was the chains, which are worn. Turns out the input shaft bearings came apart in the gear reduction, taking out both the small and big gear along the way. It still worked fine. Big gear is about a grand on bobcat. Little gear input shaft part number 6558271 is no longer available. I have scoured the depths of ebay, every spare part site I can think of looking for that or the whole gear reduction case part number 6708266 as well. Lots of them for the smaller machines. Zero for the 853. Any ideas? I've considered building the teeth up with the welder and grinding, but I know it wouldn't be as strong.