Don't think that has changed between the 80's and 90's. IMHO they had the head plug leak and got run low on oil, or whoever repaired the head plug used too much RTV and plugged off part of the passages to the cam lubrication system. There are instances of RTV being used to excess on side covers and the extra coming off and plugging the oil pickup screen on other bikes and even some cars/trucks. Too heavy an oil in cold weather will also cause the fresh oil to reach the cam area late in the process and that could happen with someone starting one with 20W-50 in it on a sunny but below freezing winter day to "warm it up" .  Also when oil overheats (above about 225 Deg F for dino) it oxidizes and becomes very viscous, to the point of being almost solid when cooled. For years I had some oil from a Chevrolet V-8 engine that the owner didn't believe in oil changes. 2 weeks before his annual vacation his Station wagaon came in on the hook. engine was siezed and I scrapped the oil (?) from the pan and put it in a stryofoam cup so I could use it in the classroom. I could put a wood pencil in it and pick up the whole cup, it was that solid. I had that sample in a peanut can from 1974 until I retired in 1998. It went to and from Europe with me when I taught over there and then to Alaska. It would sit upside down and never run out of the cup. So old dirty oil overheating could also cause the head problem. I've never heard of a shop that could bore the head and provide a substitute bushing to run the cam in, but it has been done for other engines and a good machinist could probably set and do the first one in 1/2 day. The rest would be quick and dirty. There must be more than a few bad heads around if one could round them all up and get them to one machinist it would pay. I haven't priced a new bare head but I would guess it would in the $500-800 range. Max

It's not just a "here's the cash, gimmee the title & the keys." transaction? Maybe you can hand him the cash at the same time he drops the key in your hand? Keep a few bucks, holding them hostage, till he gives ya the title?

Have you considered draining the oil & seeing if it's full O metal with a magnet before you drop the $$ onit?  All you need is a 14 mm & a pan & a couple O quarts O oil. If you decide you dont want the bike, you wont even HAVE to use the oil I guess. But I would replace it for the guy if I drained it. I take a plastic bag from the store & put my hand in it & keep the oil off me while I back the plug ouit.  I still need a rag, but I am not quite so nasty that way. Just a thought. Maybe a dumb one I dunno.,