So, actually got round to doing this yesterday on what seemed like the first dry day of the year. Just went with opie's recommended in the end, febi bilstein 21829, which I think may be oem as the bottle looks suspiciously VWAG. Anyway, doing the job was piece of cake, drain/fill plugs are very accessible, you only have to raise the car just enough to get the undertray off. Unfortunately, not the improvement i was hoping for. Only slight improvement in cold shifts, still a bit notchy but not as "crunchy" at certain rpm. Overall though, does feel a bit better when fully warmed up. Worth doing for £50 if your happy to do yourself at home but probably wouldn't bother with the hassle/cost of getting a garage to do it. Regards mileage mine has just shy of 30k on it.