Sorry for the delay in repying; as you have discovered, we don't get much traffic on here.
I've only ever had the top end off, so can't really help with the bottom end.
The bush in the clutch casing is a known weak point, and wear results in loss of oil pressure. Some have replaced it with an oil seal, but it needs to withstand full oil pressure, as the oil gallery is behind it. It's never going to work well with a bush, as it can't be guaranteed it's in line with the crank, and of course there will be run-out on the crank too. I don't THINK there's a sludge trap, as the strainer should be designed to eliminate the need, but I'm not sure. The manuals and parts books are available via links in the Links section. Only the rider handbook is available in English. Workshop Manual is in Italian, but has many diagrams and dimensions.
Glad you got the pinion off OK.
Also on the links section there should be a link to the advrider thread by Leafman, which gets a lot more traffic than here, and some serial engine workers who should be able to help out. I'd try there, in case nobody chips in here