A few years back a colleague had an MGF he had so many problems with it he almost went insane ! That's what made me say no to her.
Everyone will tell you that the K series eats head gaskets, but I think that wasn't really true. Not on the ones I owned, anyway.
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That's the first thing that went through my mind, but I know there is a conversion kit to avoid this, but really don't want the hassle.
Conversion Kit? There's no need, as long you do the job properly: use a good quality gasket(either of the commonly suggested types will do), skim the head, and most importantly check the liner heights and shim them as necessary. None of that should be difficult for a competent mechanic.
Biggest killer of MGFs is now rot in the sills and rear subframe mounts.
As for problems to drive you insane, buy a Boxster. Although there's a really good chance of an unplanned off road excursion with one of those.