40k is getting up there but depending on the condition of everything else it might be worth a go. Suspension will be pretty rough at that point so that is something to consider. there is very little on a 748 of that vintage that will go catastrophically bad outside of the belts and rockers. The plug for the charging system always burns up giving inconsistent electrical issues and the fuel pump and lines will need to be addressed. I like to offer the seller a free oil change with my inspection, I tell them I would like to check the screens and will change the oil and filter for them, if all is good I buy the bike, if not I let them know what's wrong and they get a free oil change. I have only had one guy pass on the offer. the few that had obvious signs of rocker flake the seller understood and discounted the price to where I couldn't pass up. best case scenario is you put a weekend and $1000 into it for a tune-up with belts and rockers and have a cheap(?) good 748, , second best is you need to put a replacement engine in it, there are plenty available in all the different displacements for cheap, worst case is you bought it for less than the sum of the parts and have to part it out to recover. depending on what you spend to get it you are probably safe if it is a "too good to pass up" deal.