I have the same problem, i spilled oil over my keyboard. Since that some keys need to be pressed a lot harder to work as normal. I already took of some of the Keys to clean below. Which helps a lot, for a couple hours they work fine.

But after a they return to their old status.... I guess that there is still oil that gets back an between the contact under the keys.

So i guess i would have to clean in between the layers of the keyboard.

Can i get in between the plastic foil and the contacts by disassembling the keyboard?

As well if you would recommend to replace the keyboard entirely, which is the repacement keyboard that corresponds to my one?

I have an Early 2011 MacBook 15"

Thanks for any help!