The rear hub is simple to get off, but preparing it for powder coating will be a nightmare. You’d need to split the drive having drained it of oil. Then you’re going to have to remove 4 bearings the axle seal, pinion gear and the rubber bush at the torque arm linkage.
Then it needs carefully masking off so as not to coat any bits that shouldn’t be (like the insides). Powder coating itself shouldn’t be too costly - £80-100 I’d guess.
Then you need new bearings....
2 of them are cheap - around £8 each. The pinion bearing will be more like £30, whilst the needle roller bearing on the axle is nearer £50. If the main crown bearing also needs replacing, add another £40.
After installing the pinion bearing, you need to adjust the backlash between it and the crown gear - new shims may well be needed for that, only available from BMW, cost unknown.
A new axle seal will be £25 or so. The rubber bush should be cheap but installing it will be painful.
And of course, it’ll be £18 for a litre bottle of gear oil. That you’ll use 180ml of.
All in all, it’s quite an undertaking.
