My daughter's having trouble with a front seat belt on her Mondeo. It won't always 'click' in. I see the problem end includes the pre-tensioner.

I presume this pre-tensioner is an explosive device and as such should be treated with great care.

Is it acceptable to just change one part of a seat-belt? There's something in the back of my mind about the two parts being a 'matched pair'.

They're dirt cheap on ebay, but if I obtained one would it need a 'black box' re-coded to recognise it?