I'm in a 2005 MK1 1.2 (3 cylinder) and I've got a dodgy coil pack, but the car's done 155K (I think they're the originals)

Do I replace all 3 or just the 1?

I didn't know if the others will be on there way out

 

Cheers & all that

Replace 2, keep the non-failed original onboard so you can swap it in for any other one that fails in future.