Seat busted, MOT failure, to repaire or to replace?

[Thomas77GR]

Hello
My driver's seat is broken underneath on the side next to the middle console (the break is I think between the seat and the rail) which means that you can rock the seat easily (lifts a bit on the rear left corner) even though the securing bolts are tight.

This has resulted in a MOT failure (along other problems). The garage basically told me that they can't be bothered to fix my seat and told me to sort it out elsewhere.

So what can I do? do I need a new seat? I have the beige leather type. The seat leather trim is actually fine which is a shame if I have to replace the whole seat. Can I just swap the under frame/rail for the driver's seat? would the rails off another vauxhall fit?
what about the pretensioner - I haven't looked there but by reading on the net I think I need a plastic thingie/fork in order to take y seat out for further inspection?

Can I just wrap a zip tie around the busted area and secure it like that just to pass the MOT for now and then look at it at later stage?

I am based in Scotland, Aberdeen.. any Cali owners up that way that could call round and share their wisdome with a novice?
thanks
Thomas

[v6 steve]

take it off an get it welded up, the plastic fork should be on the back of the pretensioner its red so you should see it ok