Hi, first post for this forum.
I am experienced in CAT Grey Iron. Dealt with C's and D series grey iron stuff.
Have also had a lot of dealings with 308BSR, 308BCR, 313BSR and compatible stuff.
The C series and D series grey iron do differ a lot, but mainly in wiring, slight engine parts, some pumps and hydraulic parts are different and most of all, the arrangent of the tractor is different to that sold and serviced in known Cat territory outside of Japan.
These machines are "only" made for the Japanese market, that can source parts directly from their own parts marketing.
This is why there is problems when sourcing parts outside of Japan.
The only advice I can give, is to ask to for the English Parts / Operation books for the equivilent machines in your territory.
You will have to use a serial number prefix that is usually found in your territory, as the Japanese Serial numbers don't have an equivilent to Overseas areas.
You can buy the Japanese Parts Books, but it is very difficult to find some machines though. You then have to use an English book and the Japanese book together and make sure the parts you want, don't differ.
Some things that are "japanese market" only, usually a locally ordered equivilent will sometimes do (eg lights, mirrors, seats, hydraulics hoses, some filters etc etc)
A lot of people complain that "I can't find parts", but no one looks outside the box. Use what you can off an equivilent model numbered machine from your territory area. (keep an open mind)
Fortunately, some D series excavators, Cat are only just supporting the Grey Iron now (as in the last few weeks/months). Very slow on the uptake, but that's what you get.