Cannondale headshok - disassembling the oil cartridge?




I'm overhauling my 10 years old DD 60 headshok (it has never been
serviced before). I took out the oil cartridge, and, besides of
changing the oil, I'd like to replace all the seals with new ones.
However, I'm not sure on how to get to all of them. Specifically, my
main problem is with the seals in the upper collar. In order to replace
the seals, I need to remove the collar from the piston rod. However,
this collar is between the piston (bellow), and the large disk that
connects to the fork outer part.

Has anyone here ever done that or has any clue? Do I need special tools
for that?

Thanks in advance,


P.s. I also found out the the elastometer disintegrated - it came out
in several parts. Is this just a matter of old age?