Sorry, I somehow managed to miss this thread when I've logged in over the last few days. Glad the dealer was helpful. They did offer the 105 MultiAir in the MiTo but few were sold here. Most people seemed to go with the non-MultiAir 1.4 (78 or 95bhp) or the MultiAir Turbo 135.
It does seem mostly the 135 and 170 MultiAir's that the MA unit goes on, but that might be down to sales volumes as much as anything else. I'm sure at least one person had a problem with oil round the spark plugs on their 105 MultiAir Punto, which I believe is linked to MA unit failure, but if it's working again now, just keep an eye on it. It'd be running rough all the time if it'd failed. The dealer should have a log of the cars visit now, so if it does fail down the line hopefully there should be no fuss getting it replaced FOC - they cost about £900 otherwise, from reading about the Alfa failures.