My back box has corroded through on the outer skin. It isn't blowing as the inside seems intact. Would you get it replaced or will it be ok just to leave it?

I would wait for now until your next MOT if only the outer skin, but check the rear mounting brackets/straps are secure and not corroded as they can rust through, break and cause damage to the rest of the exhaust system if it suddenly drops down as the back box is heavy.

I'd use it as an excuse to fit a Milltek :).

I've just had Masterdriver near Aylesbury change out my original exhaust on a 2005 Cooper - mine had also rotted through the first of the two skins. I think it was blowing a small amount. I didn't want a chavvy "boy racer" exhaust and was not paying the £300odd that BMW Mini wanted.

The guys at Masterdriver offered me several options from a range of exhaust makers (one very cheap and mid-range at around £150ish). I went for the mid-range and it's hard to tell from the BMW part (apart from the rust on the old BMW one!). On the way home, I swear my MPG was 5-10MPG better!

Woukd definately recommend this independant MINI garage to family and friends.