Hi Gibbo.
Mostly boredom I presume. You have had some good advice here. I would add that you probably need to check for wear on the cush drives in the rear wheel hub. They do seem to go quickly on some bikes. Perhaps you should ask the seller for service records or major work carried out. Other niggles can be rectifiers, wiring faults and frame corrosion. For 4k, you should be looking at a bike in very good condition.

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'09 Black XT660Z
Mods:Acerbis handguards, MTC carbon can, DNA stage1 Filter upgrade, UFO high fender, Nuvi310 Ram Mounted

Machines of my past: DR 350S Zebra, KLR650 with touring mods - 35000km Southern Africa in 1 year