Fuel injection pump cleaning

Still looking for some experts here, can anyone recommend any videos, articles, or instructions on how to tear down these units and then build them back up? I've taken measurements to be able to set them all back to their original settings (not going to remove the gear from the piston) but was considering removing the threaded bore. I'm also curious about what looks like an o-ring gland at the base of the pump - there is no call out for an o-ring here in the parts manual and there were none when I removed them. Given the amount of rust in that location I'm thinking a o-ring would be a good addition provided it doesn't interfere with seating to the pump housing.
I have read through the Servicemen's manual for the fuel pump assembly which centers on the housing and adjustments, but it doesn't talk about the individual pumps which seem to be considered a bolt on part. There is a small adjustment screw on the pump, is this a bleed screw or is it used to tuning?

there is a separate book for the engine and the fuel system itself it goes into more detail. tha screw with a flattend oval head is the bleed screw. the tool is available from cat except its a socket not a spanner chapter 19 does sell a reproduction spanner.