my experiences anyway
The manual and the tuning guide online had two different numbers, 20-40mm and 45mm. I emailed marzocchi back in 2002 for an answer and never heard back. Either way, the only numbers I ever saw were in mm from the top of the stanchion, not ml, so I would guess the 45 you have is mm.
Either way, I ran mine for 2 years with about 35mm from the top. From experimentation that worked best, you may want a little more or less (more oil/less mm if you bottom easily, opposite if you don't get full travel). That number is measured with the top caps off, fork fully compressed and from the top of threads for the top cap down to the oil level.
For general tuning, my x-fly always had a little more stiction than I liked. Stay with golden spectro 125/150 (what marzocchi uses), I tried other brands and none worked quite as well. Also, if your fork is anything like mine, it helped if I pulled off the lowers and put slick honey on the seals from time to time, as well as using triflow before every ride. Both of those tips come from Marzocchi documentation.
Oh yeah, although I got free marzocchi seals for my xfly while I had it, I use enduro seals on my super-t and I like them better. If you need new seals, that would be the way I'd go.
