Spare parts are not too bad to get hold of,some parts you can get new off the shelf.
I am a committee member of the Caterpillar "Link " club,we have around 300 members in the UK.We tend to help each other out with regards to information and spare parts to keep these old Cats going.I have a Caterpillar D2 built in 1938 and a I H TD6 that was a lease lend machine in WW2.
Photo shows a Caterpillar D7 M belonging to Rus Saywell.