If recall correctly without looking the breather pipe is inline with and below the ECU, in severe cases this can get filled up with oil emulsion that could cause you problem althtough i have never heard of such a severe reaction.
For such a situation to arise I would be thinking more along the line of sticky piston rings allowing the compression in the pots to reach the sump .
I hope I'm wrong, it is worth checking the crankcase breather pipe first
You don't say what happened after you replaced the oil?
Bearing in mind the sump only holds 4.5 litres to start with .
I trust the sump wasn't heavily overfilled that would also cause your problem
This photo on page 38 shows the pipe concerned .I would be inclined to take the ecu off and make surethe pipe marked (1) clean I'd use another piece of flexipolythene tube to ensure it clear. rag for cleaning is not a good idea for cleaning in case it gets hooked on obstructions.
http://www.aclassinfo.co.uk/DSC08603.JPG http://www.aclassinfo.co.uk/mypage.38.htm
Please don't forget the feed back, we don't want to encounter this one to often makes the engine messy.
Just as a point of interest was your dip stick fitted and pushed fully home?
