I have a similar problem on my 06 E350 - I have looked at a new pump both in the MB Parts System and others and it looks like there's only one fuel pump - what do you mean about doing both sides? Looks like the pump has a cover with 6 M5 screws, then the locking ring and the fuel pump. Guess I can remove both and see what's there but I'd prefer to know what I will find. Please explain "both sides". Thanks -