Bob,This is an well known problem with coras and merivas,check out vauxhall owners network.co.uk it has lots of info on this problem,i have a (04)meriva and had this prob about a year ago,it's something to do with the gear linkage that was made of plastic(a design fault)and can be replaced with a metal part that vauxhall now supply(for a fee ofcourse) ,a local garage done it for me(the mechanic was familiar about the problem) i was charged £110 supplyed and fitted,i'm told it's a bloody pain to do as it's very hard to get to...hope this helps a bit.