I recently purchased a late model D2 5U17xxx with a 24 volt direct diesel engine start. The master clutch was stuck in the engaged position, and I was unable to free it up with penetrating oil so I had to winch it on the trailer and bring it home for repair.
Apparently Cat used the same flywheel housing on the later D2s regardless of whether the tractor was a direct start or had a starting engine. Mine has a flat plate where the starting engine would have been located and the two 12 volt batteries connected in series sit atop the plate.
There is a water jacket in the flywheel housing that is used to help cool a starting engine. Apparently the gasket and plate sealing off the water jacket failed and coolant ended up in the flywheel housing and the clutch compartment. All of the master clutch parts were heavily rusted and took much effore including heat in most cases to free up and separate the parts. I'm planning on using CRC Rust Converter on the clutch parts to provide some rust protection.
There are drain plugs in the bottom of the flywheel and clutch housings. I have seen the drain plugs drilled and cotter pins installed to allow any accumulated fluids to drain. Is that a recommended practice?