Monitor Audios customer support is excellent.
Give them a ring and ask about any bits you need because something is missing/broken.
I took my centre speaker in (I live 10 miels away) because I was suspiscious of the crossover. The dude rigged it up to his thingamy (out the back somewhere) and produced a frequency response curve, plotted it compared to the reference... it matched showing my speaker worked fine. I asked if he could re-attach the tweeter guard which had come loose, only held on by the magnetism. He said it was the wrong size one, not sure how it got there (second hand speaker). He replaced that and
without me even asking replaced the front speaker grille, which was a bit loose, letting me keep the old one. This was for my gold reference centre.
As it is, so long as it has been working a while (i.e. it's proven) and you take care of it you'll get years and years out of your MA speakers (much like most other speakers), way more than a 3 years warranty. I'd be suprised if any faild before that was up - unless they failed in the first couple of weeks or you're a total psychopath when it comes to stressing your speakers - I mean full amplitude square waves psycho!
Disclaimer: Full amplitude square waves through your speakers is a very, very bad idea.