Nice piece recently seen at an auction place. This is maybe rather a machine for a museum or as exhibit for a machine dealer than for bringit it back to work. We guess even for this machine CAT will still have parts for sale. Inspection of used track type loaders, track type dozers and any other machine can be performed by: http://www.mevas.eu/equipment-inspection.html
Those first two pictures are of a 933, not a 931. I agree that it's a nice looking machine. Are the machines in Germany or the States? I don't recognize the brands of rollers in the background so I'm thinking they're not here.
We've had 3 931s like that, I like them for that age and size. My grandpa had a 66 model 933 like that, it will sure keep you busy.