You can also get little rubber rings that go on the underside of the keys to prevent that plastic on plastic action when you bottom out the keys.
They make pretty much zero difference on my K70 with browns.
I've just noticed why my refurbished model was, well refurbished, and I suspect it was an RMA rather than refurbished and then sold on... the number 4 on the numpad is nearly always a different colour to the rest of the keys.
I've not tried programming it yet to see if that affects it (fully expect it will), but perhaps the switch was installed 90 degrees one way or the other, meaning the colour contacts are all wrong.
This isn't the first time I've had dodgy "refurbished" goods from Corsair. I bought a USB stick refurbished last year and it stopped working just outside the 3 month warranty period. Neither the retailer nor Corsair were interested and as I bought it through work so I couldn't claim through the sales of goods act either. I've had a lot of luck with refurbished goods going back years here as well as in other shops (in fact no problems at all that I can remember) so I'm not impressed with Corsair in this regard considering 100% of the refurbished products I've bought from them were either not as sold/not checked or plain known faulty.
Still, it's taken me a couple of weeks to notice this, so it's not going to bother me considering I rarely use the numpad unless I'm working with spreadsheets, and I'm hardly going to programme in keys for that.