I've just given my bike an oil change after 1000 miles (3000 miles travelled).
I removed all filters (tank, sump plate and oil purifier).
I can report that there was no sludge at all, anywhere.
When I rebuilt it some years ago, I fitted a cartridge oil filter. Although I have changed the filter on a previous occasion and changed oil after 500, 1000 and every 1000 or so, this is the first time I remove the oil purifier cap.
I think that the lack of crud in the purifier vindicated use of the cartridge filter (it is in itself not an expensive item) which tucks away neatly between the gearbox and engine bottom end, so it's not really visible.
BR to all,