paddyb - is the sound affected? If it is, and depending on what you paid for the speakers, you're better off just buying another pair. Because I suspect replacing the tweeters will cost more than what you paid for the speakers themselves.
If they still sound good, then just leave them be.
My nieces pressed their fingers in the tweeters of my 685s, and replacing them cost me nearly a third of the speaker, but I had no choice.
if you can get to the back of them,i recently repaired a mission 752 tweeter by pouring in boiling water,4 separate fills for around 4 min.combination of heat and gravity has left the tweeter perfect no dimples.