Just my opinion. Seller should be banned as it does appear that the car was purchased in good faith and based on seller`s description which, to put it mildly, was misleading 
Coming to all this rather late in the day. Whats misleading about the add? Why should the seller be banned?
Ultimately, buying and selling anything, anywhere, the rule remains as 'caveat emptor' - buyer beware.
Diane - its fine stating that you will not reduce your price below what you paid - thats fair enough - but I cannot see anywhere what you actually paid. Your business (and the sellers), no one else's. If you are selling, then a full and fair add would go a long way....
My tuppenceworth remains the same. You bought it after perusing the forum to gain an insight into the marque. You have asked questions of many, recieved info and advice from a lot, and offers of hands on help from several. I say you will have the better car for getting it fettled whilst you are away in a hire car to france or, indeed, when you return so you can oversee the work. The final car you run will be all the better for it.... 
"i then bought it from him in October 2009.
It has full service stamps up to 74,000 miles. Has just had a genuine GM cam kit fitted. There is no need to do water pump as it does not run off of the cam belt but an auxillory belt and i was advised by Vauhall technition not to change."
If that`s not misleading what else do you call it. The seller has implied new cam kit just fitted, very doubtful with no documentary evidence to support. But as you say "caveat emptor"
It says service history to 74k.
It says genuine GM cambelt kit fitted - be that heavily cash discounted, 5 finger discounted or whatever - and 'just' fitted. That could mean 5 minutes ago, 5 hours/days/weeks/months or whatever the seller/buyer AGREE to, not suppose/assume without further enquiry.
Selling is different to buying, hence Caveat Emptor...
As said, cant see whats misleading - but can see where someone can see but not read whats there.....