I'm checking out a mid-70s Case 850 dozer with a 6-way blade and 4-cyl diesel. Last year it lost power from a hot torque converter, after sitting for a year, I added fresh fluids and new batteries, it started but soon developed knocking and rough running, and now the engine won't turn over. Oil looks thin and gray, so could this be spun bearings, or might something in the torque converter gears be the culprit? Should I consider a used motor or repower?