Seems to be trans fluid leaking and the owner says he had it in the shop about 10hrs prior for the right side leaking and it was just loose bolts. It has a leak from what I believe to be the transmission / left final drive joint. I put the machine through its paces today for a good hour.

The U shaped metal strut on the rt hand side with the two bolts is your service strut when working on the unit with the loader raised, unbolt it and place it on the lift cylinder rod while working or servicing with the loader up. I would do the two top loader arms and tower pins first and try to get some of the side to side travel out. The machine has some age but still has life left in her, most will need some pin and bushings to tighten them up. I would also check both final drive lube levels and note the condition of the lube.

I would run it some and watch your gauges and oil levels. The machine looks like it's had some paint, can't really see the track system, pin and bushings, looks like a loose pad on the rt and a little heavy wear on the rt sprocket, idlers have some adjustment left looking at the bolt stops on the truck frame. They made some changes in the later series, C/D to wet brakes and the cummins engine. They are a good size machine around 75hp, and 20,000 lbs.

850b case dozer specs