Do not change the Crank Angle sensor until you have removed it and cleaned it physically. Exactly the same way you mentioned, with carbie cleaner or better still electrical contact or circuit board spray cleaner.
I have cleaned the CAS in my 2001 Scenic Rx4 2 times and have not had any difficulty doing so. Renault must make a killing on this proceedure. The CAS are not cheap and I'd bet my car on the fact I think only 10% of them are CAS faults.
The second problem could be the connector. Renault actually changed the connectors a couple of times until they got it right. I have a friend with a 225 Megane turbo that had the same problem and they did the CAS and connector change and no problems so far after a few months. His got progressivly worse until he couldn't start it at all.
Do an ebay search for CAS and you'll see the different types for Renaults available in the UK these days and i think some ads even mention the later connectors.
good luck,
Chris
(Australia)