Is there a tutorial anywhere online or alike to overhaul this fork, or a general tutorial for marzocchi forks? The manual doesn't say much about the internal maintenance.

It still has the original oil inside from 2003. But I haven't used this fork since 2005. I was thinking of replacing the oil. It doesn't leak nor do the stanchions have any play, so I assume the bushings and seals are still ok.

Is it bad to ride with old oil?