Hi,
I reused mine - mostly because the idea that I should replace them didn't really occur - with the MM 2-in-1 exhaust with about 1500miles on the clock. No problems so far (~3000km later) other than the exhaust pipes looking bluey-purple. Not sure if that's good or bad but it's working fine. Nice crackle on the overrun

which is a bit of a giveaway when you see the Spanish cops with RADAR...
The only thing that annoyed me with the MM (other than wasting an hour before realising that the exhaust fits inside the frame) is that I couldn't tighten the inside bolt on the right hand (looking from the front) exhaust manifol clamp thingy as the header pipe is in the way. Hasn't been a problem so far.
Cheers,
Ian