Help with cleaning intake

[grokicki]

I have a 94 e320 110,000 miles

I removed my intake duct that runs over the engine to the throttle body and noticed it has a black film of oil in it and the throttle body is quite dirty. I want to clean these to try and help my surging issues. So after reading for hours here I will perform the following:
-Clean MAF
-Clean Throttle body
-Clean intake duct
-Change plugs to f8dc4
-Change plug connectors under coils
-Clean EGR tube

Some questions:
What do I use to clean the MAF and how?
For the throttle body I read here to use brake cleaner, and then spray with WD40. Is this correct?
How is the oil getting into my intake duct?
Also what is the sensor that plugs into the intake tube before the throttle body and how to clean it?
Do I need to replace the rubber seals that go from the intake duct to the engine?

Thanks for your help.