Nope no wobble at all, the TomTom still fits snugly in the cradle, it's just loosened up ever so slightly that I no longer have to strain to pry it out
Tried the magnet modification today. However, when fitted I was not convinced the magnet would hold it, despite it being quite a powerful magnet. So I just thought sod it and went for it, and got it to fit in the original cradle, a bit of furniture polish to lubricate it and it went in no bother. Thanks for giving me the encouragement to have a go. It slides in and out quite easily. The top part of the mounting has a soft rubber lining, so damage is quite unlikely.
Jobs a good un. Thanks.