So I bought it.
It was a little more than weeping, and the chain was loose on full extension. Exhaust to barrel joint is a bit oily but other than that is seemed reasonable for the years. Front suspension / head bearings seem good, rear suspension good. Brand new tyres and brake pads are in good nick. Clutch wasn't clattery so good there, however starter motor didn't work! I'm not too bothered about that as she started on first kick (cold engine) but then needed to warm up a bit, before taking any throttle. Once warm, pickup and open throttle was very nice. Plenty of power down the bottom of the rev range and at the top.
All good fun, I just need to get it home. The obvious way is to just ride on the road home (ie on tarmac, remember this is Kenya and there are thousands of small bikes riding around in a dangerous state, although most have number plates), although I could ride on the back roads (ie off road) all the way home.
Just slightly worried about that chain!