Bought a pair of used Dura Ace carbon wheels a few weeks ago. Going over them today to mount some tires I noticed the free hub was really rough. Took the hub apart to find that water had gotten into the cartridge bearings (this model had cartridges in the freehub, the wheel bearings are cup and cone) and they were pretty rusted.
Took a look at the Park website and they note that the freehubs, according to Shimano, are not rebuild-able and are a replacement item.
Popped the seal out, matched a socket to the backside freehub "axle" OD, heated the aluminum body up a bit and whacked it. Out pops the outer bearing. Cleaned the inside of the hub to find a clip holding in the inner bearing. Popped that, whacked it again and out pops the inner bearing. Another whack got it past the outer bearing seat.
Cleaned it up, greased it a bit, and popped in two bearings I had lying around that matched.
Badda bing badda boom. $20 vs $200 and smooth as can be.