I still miss my Mk1 on twisty backroads.
One thing to look out for is the front sprocket. They had a tendancy for the sprocket nut to come loose when aftermarket sprockets were used. The sprocket won't come off but the nut rattles around on the shaft and can damage the threads, although the nut is a lot softer than the shaft so you'll usually get away with it. This has led to a few having the sprocket or nut welded or threadlocked on, and might be tricky to get off when you need to change the sprocket. Someone on here found an alternative thicker nut which is a sensible upgrade to give it a bit more thread to hold on to.
Mk1's use oil, they all do it and isn't an issue if the owners keep on top of it, but if it's been left to get too low at any point then it's likely the bike will burn a lot more oil as it wears the bores. I honed the barrels and fitted new piston rings and valve stem seals and it made a huge difference to the oil consumption.
The gear box is supposed to be a bit clunky but check 3rd gear works ok, as that's the one that will start to show issues if the gearbox does have any problems. Mainly only an issue on high mileage bikes though.
If it's running a bit rough and burning more fuel than you'd expect then the emulsion tubes could be worn. Factory Pro used to make a hard wearing replacement, but not sure if they're still available. A search for Factory Pro or Emulsion Tubes on here will find you a few threads on changing them
Edited by ChrisG, 30 September 2020 - 10:38 am.
1992 Mk1, 76k miles, Hagon springs, MTC exhaust, 4½ gears Gone now
2009 900 abs, 42k miles, Yamaha heated grips, double bubble screen, R&G crash bungs, scottoiler, Autocom, 1500 lumen LED spotlights.