Hey Nige,
I've been thinking about it and given that the present one has lasted 11 years I don't think its worth the extra expense of getting a stainless one.
I am going to do one for the Scammell however, and have been meaning to ask you about the down pipe, because I remember you making one for Emmas munga, did you get that done at Top Gear? I had always presumed you had made it yourself.
Cheers, Rich