I think I have the same problem as the OP but with an older version of the k70.
1 year ago some of my keycaps started to break, i made a ticket to get a replacement... after months of waiting and a lost parcel i got them, but.... other keycaps are also breaking (like 6-7 already, one of them today) and my warranty is over (+2 years).
Too bad they are using such a bad plastic material.... I really did nothing special with the keycaps, no o-rings, nothing droped, cleaned them with a bit of water.
photo with a broken keycap:
http://imgur.com/SCwTIIt
Guess I'll have to buy another keyboard...