1. I would be suspicous of the hourmeter reading - hourmeters can be changed from time to time, exchanged for a alower reading meter, and original OEM hourmeter would hav the CAT name or logo on the face. 1800 hrs on a machine that is at least 16 years old makes me that way - a serial number would validate teh exact age. It should be like new unless it was used in a "pickle foundry".
2. If the hours are accurate then $6K is a decent price.
3. I would ask the seller if they have service records on this machine.