Bit late on this topic I know, but thought I'd throw something in here. My '61 Flash was built at a time when oil wasn't as good and there were no paper oil filters (which we all know). I also reckon owners weren't as conscientious as we're being now and left the oil changes for much longer than they should - but the beasts did keep going. So, the bikes are now rarer and not two-a-penny as they were. For me, I change my 20/50 every 1200 miles and/or annually (would like to get more mileage in but not always possible!!). I have a magnetic sump plug that catches a small clump of iron filings. For extra cleanliness, I use a large medical syringe with tube attached to extract the contents of the bottom of the oil tank (the bit that doesn't get drained off), then use a magnet and clean rag to get rid of the minute amounts of slightly gritty residue at the bottom. For me, this should be enough rather than faffing around with extra filters. I also agree with muskrat in not starting the bike unless it's going to get a good run!
Couple of questions though. #1 Has anyone come up with a paper filter element or set up that fits on/around/replaces the existing 'tea strainer' arrangement and, #2 Would a magnetised version of the 'tea strainer' provide extra protection like the sump plug does (although this would be much harder to clean). Perhaps for the latter a magnetised 'tea strainer' covered with filter paper in cartridge form.....?? Any thoughts....?