I have done the same thing recently the regulator ( Valeo) is barmy money from MB over £200.
I got mine a Valeo the same for £30inc delivered and new from Germany.
Once you have undone the cover lower the motor out and check the bearings and bushes whilst you are there all replaceable cheaply.
You cannot change the bearings on these motors, the brushes yes
Oh yes you can (In true Christmas Panto style) they (bushes) are crimped in but can be replaced.
You need to swap to oilite or for someone with a lathe access its much easier to put a small bearing in,
http://www.bearingboys.co.uk/Oilite__Bearing_Bushes_-1011-c
I think theres some on EBAY now as well
Or went to an auto electrician who kept bushes in a jam jar full of oil ?