Good (for us) to know it wasn't the fault of the Monster. $125 for a servo that crap's out on you isn't cool. I would still see if they might warrenty it. It is rated for 6v right? If you have to replace it,
these have always done the trick for me and priced right that you can have a spare or two on hand. If you're really strapped for cash (or for that project you don't want to sink a bunch money into right away)
these will do the trick but have been known to oscilate a little when returning to nuetral.