I have a G-reg one of these as a runabout. I replaced the rear shock about 5 years ago with one from a breaker on eBay (a good source of spares). It was a b@$7ard of a job as the linkage is quite complex, and it's spent years under the mudguard getting drenched in mud and water. The only time it failed the MOT was last year and related to this - There are a lot of bushes in the swinging arm/rear shock, and these will wear. Just tightening the swinging arm nut will often take up some slack. A local mechanic made me some new bushes so the price wasn't hideous (I am a skin flint). There are 4 rubber tubes joining each of the carbs to the engine and they become hardened and crack, with the potential to allow air leaks and spoil the tuning. They can be over £100 for a set. However often the cracking is supeficial. I have found getting the carbs on and off a problem, I think Yamaha got 4 carbs then built the bike around them! It's just passed it's MOT again this morning. Phew! I have had two exhausts on it over the years, second hand 4 into 1 Neta. They do seem to corrode quickly around the beginning of the silencer, though sometimes a bit of welding can prolong it's life. They are not cheap, if you can even find one. Other than that, it's just the usual stuff that goes with old bikes, fork oil seals, flaky wiring, brittle plastic bits etc. Have fun but be careful!