Hi Pete1984.....probably a bit late but figure I would post in case it helps anyone else.
Draining and refilling the oil IMHO isnt really enough, you really need to get both gear cases (both pulley and PTO ends) off and inspect the insides for any possible wear/damage.
To get the pulley end off does mean removing the pulley though so that in itself is a reasonable job. If you arent bothered about keeping it you can if very very careful cut and die grind it off.....though you have to be extremely careful not to damage the input shaft. Renting a pulley puller is probably most sensible for DIY.
Once the gear ends are off clean it all up (brake cleaner or similar probably best) and inspect all the gears for wear. Also check the plastic pulley coupler on the pulley end for wear. Doesnt need to be replaced if it looks OK....typically these dont really wear as long as the gear oil hasnt run low in the pulley end case. Also best to check the rotor condition and check for any play in the rotor pack (which might point towards bearing wear). If either of the gear casings has run low on oil it could point to a bearing seal failure on the shaft (I.e. the oils been sucked into the charger) so need to tread with caution of so.
If it's all OK, put the gear end cases back on using Loctite 574 anaerobic sealant (expensive but the thing to use) then refill. The various instructions posted on the internet give the approx amounts needed in each end but probably best just to fill each end until it comes out of the drain hole...slightly more than necessary better than not enough.
Replace the pulley (if you used a decent puller the original shouldn't be damaged and should be able to be pressed back on with some reasonable force once heated a bit in an oven)...alot of people at this point choose to put a bolt on reduced pulley on seeing as its easy to do whilst off the car.
Then a case of putting it back on the car. You really should replace the water pump as a matter of course and naturally replace all the gaskets (so the green horn end and metal one use ones), the water pump o rings and whist at it you should replace the dipstick and crank sensor o rings as a preventive measure seeing as you have the car in front end service mode. I'm pretty sure the pipework between the charger and the bypass valve at very least also needs new jubilee clips as the factory ones are single use only. On mine the pipe was replaced with a small silicone pipe that was included in the service kit along with the jubilee clips.
I can see why people swerve doing this as it's a mammoth task, and expensive if done at a garage as it's so labour intensive but it's really important to get it done. My car drives a million times better since having it done.
Interestingly many people find that their gear ends are running dry....my car was fine at 82k miles.....oil was completely black by all accounts but plenty in both ends. I guess it's all down to how well the factory gasket sealer and shaft seals have held up over time.
I think if you get it apart to find the oil has drained out of one or both gear ends it's probably best at that point to send it to someone like GTT for a proper overhaul as to replace shaft bearing seals is a professional job.