We recently bought this 300TE 4Matic with 60,000 miles on it. All seems to be working fine. However, the yellow 4matic light came on & so I checked the hydraulic level. That was down by a litre, so topped it up. Light still stays on. I haven't got underneath yet to check the transfer case oil level to see if it is overfull which would mean the hydralic 4matic system is possibly leaking. Has anybody any experience with this and what sensor is causing the 4matic light to operate? Could it just be dirty hydraulic oil?
Appreciate any advice on this, plus where do I get workshop manuals ( ? CD's) for this model?

Cheers,
Rod Barker.