I have become the recipient of a D4. The number I found on the left rear of the axle housing is 6U5036. Before I try to find an operating / maintenance / lube manual, I would like to verify if this looks like a good serial number and is the 6U the model number? This CAT has been sitting for 2+ years, so I've got some work to do in trying to get it running again. An yes, it's got that wonderful pony engine. Any help would be appreciated.

Yes that is a good SN & they were the narrow gauge (distance between the sprockets) tractor & they came out 1947 & was built to the latter part of the 50s.The wide gauge D4 was a the 7U built in the same era. They both used the D315 engine & the tractors were pretty much all the same except the width.

Its a good number standard gauge D4 built in 1950 as for the books they are always on EBay

SJ and Willie, thank you for your information. I am now able to order information that I will need to begin the work that's needed.