With the details you have given it is hard to know for sure. As you car is an early one, is it the side impact sensor? Do you have a sunroof?
It often this one
https://m.ebay.co.uk/itm/MGZTT-MGZT-...id=m4084.l1313
£30 tends to be the price they fetch.
This is a stab in the dark based on limited info you have given.
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