I clean mine up as per Marc, though I try and not take the large plastic/metal bit off as they can be a bugger, metal more so. But that same seal can be swapped between freehubs to get the correct size internal diameter.
Try the stx 7spd one, only part you may need to swap is rip the metal large seal out and put the plastic one in. No other hubs lying around?
Shame your rear seal perished, I would look for you to see if other seals fit but I'm buried in boxes at the moment