Hi Black03ar,

Thanks for your reply and suggestions. I have answered your questions below in red.

1) New Air Pump is functioning intermittently
Hmm, actually I reordered a third pump as I suspected this might be the culprit. It still triggers a CEL.
2) Ground cable on pump has corrosion (needs a good clean)
Clean as a whistle..
3) The contacts on the plug connected to the pump need a clean
Clean as a whistle..
4) Check the big 40 amp orange fuse on the top of the RCM (mine was blown, although you say your CEL is intermittent so unlikely to be this)
Yes, the orange fuse is good to go..
5) Faulty RCM - it may look alright but it is still a problem part
How do I get another one of these? Can i order off of ebay?
6) May just need a reset - disconnect the battery for a while and reconnect
How does this work? Does this work the same as clearing the code with a code reader?
7) Faulty air pressure valves - the 2 metal ones on either side of the pump - although I have not heard of these going wrong before
Hmm, can these be ordered off of Ebay? Are the expensive?