Hey Stam Hope all is well.

Did a bit of research - 2 styles - Metal disk with upper and lower brake pads(My style ) and assuming updated version with fiber disk flat upper/lower plate - 6 inch diameter for ET-B

- There is also a 7.5 and 8 inch version

I have tried to reseal these units in the past and found most times the housing was pitted and worn where the seals ride.
I normally install a new unit to save any future headaches

So...found Part # 870-900-001 (Update) would fit nicely

Thanks for the feed back :) Enjoy the day

They can be rebuilt.
Aztec will sell friction plates and rotors.
Tvh sells the seals for the slave.
The springs rarely fail.
I believe you have a 24 volt truck so you have the "small" brake.
I don't have a parts book at hand.. if you still need the number reply and I'll get back to you Monday.