nigel bishop

I'm looking for some guidance please - I have a 2005 X5 3.0D since new. I have the amber 4X4 warning light on the dash, took it to my local dealer and ran test diagnostics to find that the transfer case has failed. I have looked a little online and would like some genuine advice on where to buy replacement or if there is someone out there who can refurbish my existing box? The car still drives perfectly but now only has RWD and the 4 x 4 warning light on. Thank you in advance, Nigel