Replacing my internal speakers on mac

I spilled a small amount of water on my keyboard/ speakers, as a result the speakers wont work. (I've tried drying it out, removed the back and dried it out with a hairdryer and so on) When I try to adjust my volume, I get the little circle- symbol that says that there are no speakers connected (or something in that direction...)

Replacing it seems easy enough (I've looked at the steps) and I've recently replaced an Ipad 2 screen, so I'm gonna give this a go.

So what I want to know is: I bought my mac in 2012, so I'm just guessing that it's unibody early 2011, but how can I find out for sure? And which parts should I buy? (Left speaker, right speaker etc)