First I would like to thank everyone on this site for all of the great advice already given.  I have a D6 8U that was left behind after GW sugar went out of business about 50 years ago.   the ranch property we purchased has a old abandon limestone mine in the mountain behind my house and the last owner said the D6 was running about 40 years ago but the pony motor went out. I turned the pony over and water came out of the cylinders so I removed it.  After making sure the motor would turn over I proceeded to convert to electric start with the instructions on the site.  Everything was in great condition and looks like they had done a good job of storing it for future use. Fuel tank was full so no sign of rust but definitely had quite the smell to it. I probably bled the system a dozen times but no start even with starting fluid.   Today I ran it with the compression off until oil pressure went up kicked it over to compression and had a friend push me off a hill to get the engine speed up.  Within 50 feet it fired up and I drove it back to the shop. Oil pressure and temperature never got above normal and it purred like a kitten.  So now I'm ready to spend some money on parts and replace everything to get it back to building road's on the mountain.  I would appreciate if someone has part numbers for the valve cover gaskets, oil filters and gaskets for the fuel tower. I removed the old sock filters and installed a inline fuel filter/water separator and fuel pump to make it easier to bleed the system. I called the local cat dealer and they are no help. The serial number is 8U3924 SP.  Thanks again
 

If you fumble around long enough in the members technical library you can find a Parts Manual for the late 9U. Uses the same parts you are looking for the 8U.
I'd recommend going back to the sock type fuel filters, they have a much finer micron level of filtration than a single element filter.
Your s/n is a 1950 model.

Thanks for the reply I will get new filters. Just couldn't justify spending $100 on four socks until I knew it would run.

its not a bad idea to fit a delphi (lucas/cav) type 796 water trap filter in the line from the fuel tank this will help prolong the life of the main filters and show if you have gotten a batch of bad fuel due to the clear bowl and allows you to drain off any moisture collected there. just make sure its mounted in a protected spot.

Thanks I already added a water inline fuel separator/filter just in case of bad fuel. Ordered new sock filters but having trouble finding the fan belt. Any other tips or advice would be appreciated.

search online and at swap meet etc for a owners maintenance book, servicemans reference, and parts book to suit your machine there is also a separate parts book for the hydraulics control system and books for the engine itself.

if you have part numbers the dealers can help as some parts are still available. but they need a part number first. some of the older numbers have to be "converted" by adding a zero or 2 after the first 2 characters to make them six characters. i have found the local dealer helpful if i was patient enough to find the pn myself first.

you can get a hand primer pump for those cav style filters too. the easiest for the fan belt is cut it and take it in to a bearings and industrial supplier such as motion industries and get them to match a belt for it.

OM am i correct in thinking the 9U is the wide track model where the 8U is the narrow track. so all the engine and cooling parts would be the same with the differences being in the final drives and track gear.

I have seen some of the parts books on eBay and knowing that the 9U is pretty much the same should help trying to find parts. My wife laughed about the water separator for the fuel she said Wyoming is like a giant desiccant pad and no chance of that happening. The hurricane force winds would soak it up in no time just filling the tank.

i live in a sub tropical climate and even when we have drought you still get water contaminated fuel. as most of our fuel comes from overseas it still can get moisture in it. most of it comes from condensation over night settling in the fuel when you have part filled tanks. its minute but it still happens.

This is the water separator I installed. Looks very similar to the Delphi you suggested. We put these on all of the equipment just in case. We rarely get any water out of them but you never know what could happen.