You might want to check your battery to make sure its not pressing up as that can happen. Most of the time I find the center keys get effected first. You'll need to remove it to check it out.
The other possibility is some keys get a beating as they tend to be used more. S's & R's are two of the most used letters.
Using the show keyboard menu option by enabling it with Keyboard Preferences will allow you to buy some time as well as a way to test your keyboards keys.
If you think it's not the battery, then it's likely time for a new keyboard. You can replace the full uppercase assembly or you can replace the keyboard alone. Here's the IFIXIT guide you'll need to follow: MacBook Pro 13" Unibody Mid 2012 Upper Case Replacement Here's the uppercase: MacBook Pro 13" Unibody (Early 2011-Mid 2012) Upper Case. Replacing the keyboard alone is a bit more work and you do need to be careful in taking the old one out. Frankly, I think just getting the uppercase is just easier.
Here's an image of a bad battery looks like:
crwdns2934105:0crwdne2934105:0
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3
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Did you find an answer/ as you can see i have some keys not working.
crwdns2934271:0crwdnd2934271:0 Becca Bradley crwdne2934271:0
Sounds like liquid has shorted out some of the keys.
crwdns2934271:0crwdnd2934271:0 mayer crwdne2934271:0
@mayer definitely not the case, i have never spilled any liquid on this machine.
crwdns2934271:0crwdnd2934271:0 Matt crwdne2934271:0
i ended up replacing the entire top case rather than messing around with all the screws to take the keyboard out and replace only that...we'll see if that fixes the problem. so far the results look promising...
crwdns2934271:0crwdnd2934271:0 Matt crwdne2934271:0