bang on Gibbo
If you have the Oil Can finish, it wears and leaves raw steel underneath that rusts as soon as you wave a bit of water vapour at it.
It's supposed to increase the aount of spin and reduce glare.
Mine rust as well and they are the satin finished ones. I just clean and dry them after a wet round, but if they are left to late the rust comes off with a bit of a rub.
After i clean my wedges (MPT10), as they are prone for rusting i whipe them with a cloth sprayed lightly with a bit of wd40, not enough to effect performance, but enough to stop the rusting. i know the rust doesnt effect the functionality of the club, but i was a bit let down that my nice new wedges rusted after one round.