Disclaimer: Do this at your own risk, etc etc.
I'd had my hub for about 600kms. It had started to make some funny noises, and so I thought I'd take it apart for a bit of an oil bath. It worked a treat - it's now quieter, has heaps lower resistance, and feels completely different to ride. Shifting quality is still 100% awesome. I must stress that this is REALLY EASY - I'm certainly no mechanic.
Step 1: Prepare hub. Remove everything you can (disc rotor, cassette joint, and dust caps, etc..). Make sure you remove the right hand chain guide (plastic part of the hub).
Step 2: Get tools. These are the bare minimum: 15mm cone wrench and 17mm cone/normal crescent wrench. If you want, you can get the right hand dust cap removal tool too, though it's not necessary if you're tough (see step 4)!
Step 3: Remove the left hand (non-drive-side) locknut and cone with the 15/17mm wrenches.
Step 4: Remove the right hand dust cap thingy (the thing with the serrated edge under the right hand chain guide). This is tricky, but not impossible, without the removal tool. What you need to do is get a wrench (any size) and push one of the big grooves in the right direction (note that the thread is the wrong way around).
Step 5: Pull out the insides
So, at this stage, you'll get your first look at the hub innards. Mine (after ~600kms of hard XC singletrack kms over winter) were pretty pristine-looking. Note that there's also a tool to remove the non-drive-side bearings. Mine looked fine so I didn't bother, but you may need to buy this tool if your bearings look yucky.
Step 5.5: clean out the insides of the hub shell. Regrease the inside of the non-drive side bearings with a heavy grease.
Step 6: On the end of the non-drive side of the hub internals, you'll see a snap ring thingy. Prise it off with a screwdriver (make sure you don't lose it, it really comes flying off). Now, you can separate the shafty bit from the ring-geary bit. You can also remove the drive-side bearing race for inspection at this point. This was the limit of my disassembly.
Step 7: Put the hub in a bath of petrol (I just used normal unleaded, but apparently diesel will work even better). You can do this with the hub disassembled, or assembled, or both. Probably a good idea to put the ring-gear bit back on the shaft-bit and work the gears while it's in the petrol bath. This will dissolve most of the white grease. Leave it for a few minutes then swish it about a bit, work the gears, etc... You will probably need to get in there with a toothbrush to get rid of the grease in the nooks and crannies. Get rid of all the grease that you can see. You probably don't want to use normal engine degreaser, because you are meant to flush that out with water (hub+water=bad!!). Remove the hub bits from the petrol bath, and the petrol should evaporate pretty quickly. Decant off 99% of the dirty petrol into another container, the tip the remainder into an absorbent cloth. Look at all those metal filings - yuck!
Step 8: Regrease the non-drive side bearings with a heavy grease. Also, regrease the seals on the drive side.
Step 8.5: Put the snap ring back on.
Step 9: Put the (dry!) hub in a bath of lubricant of your choice. I used a synthetic Valvoline automatic transmission fluid, as per some other guys on teh intratubes. You might want to try something a bit heavier if you're from a warmer climate (diff oil?). Also, shimano makes an oil specially for this purpose, but it's expensive and only comes in 10 litres (you'll probably need <1 depending on the size of your container). Anyway, whatever you use, swish the hub around in the bath for a few minutes. Drain the hub a little bit.
Step 10: Put the hub back into the shell (don't forget the drive side bearings! Make sure you get them the right way, too - the shimano blow up diagram shows the right way). Screw the drive-side dust cap thingy back on, and also the nondrive side cone and lock nut, tight enough so there's no play in the axle relative to the rest of the hub.
Step 11: Have a beer!
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