Keefusb

The cassette comes off with a standard Shimano tool. I never ventured to take the freewheel body assembly completely apart. Besides replacing/re-greasing the ball bearings (cups always looked OK to me, I have read horror stories about Sovos using soft metal for the cups, but I have not personally witnessed that with my two bikes), the way I serviced the rear hubs was to shoot brake cleaner into the bodies until crud stopped coming out, and then I would drip Husqvarna bar oil or Phil's Tenacious oil down into the pawls. Compared to my road bikes, the H300's don't get heavy use, and an annual cleaning and re-lubing (I reckon technically it's not really an overhauling) as described has kept them going all these years.

It is my understanding that they can be completely disassembled by means of a deep 11mm allen/hex key, and the cup can be carefully unthreaded by fabricating a "notch wrench" out of scrap metal or gently tapping out using a screwdriver or chisel placed in the notch(es).

There are plenty of postings here and other places that warn against a complete disassembly due to a lack of replacement parts. A mistake that leads to breakage or discovery of extreme wear or damage usually means a new hub.