TBH, the wheel bearings are fairly easy to do and don't seem to give up any quicker than on any other bike. You're probably better off leaving them until they show signs of trouble. Same with the sprocket carrier bearing really. I know some have had them collapse with some disastrous results, but it's fairly easy to change and they do last if the chain is correctly aligned and cush rubbers are regularly changed, packed out or fitted with polyurethane items.

It is the headrace, swingarm, relay bearings that are the real issue on these bikes as, unless attended to early, will not last and (particularly the swingarm pivots) can be a real ball-ache to do if the swingarm through bolt gets seized in the bushes/inner races. Preventative maintenance is key to long service life. It is definitely worth putting in the effort here.

My headrace, swingarm pivot bearing/bushes and the relay bearings are all original, 8 years old and have covered about 34K miles. I can only think they've done so well because I stripped it all down and greased them at around 10K miles. I've stripped them one further time (at about 22K) and they're were in far better nick than they were on the original strip down. I also removed all the crappy MPL solid lubricant the second time round too. Both times all the seals were replaced and waterproof grease used.

I would recommend focussing any preventative bearing maintenance on headrace and swingarm/relay, especially if you don not know when it was done, if its ever been done at all? You will reap the benefits of your efforts in the long term.

Ohlins wrote an excellent walkthrough guide on doing the swingarm and relay. Have a look and see what is involved:

http://www.xt660.com/showthread.php?t=25584

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