Is it normal to just switch the bottom ones? I recently cleaned, repasted and updated my brother's cech-20XX's and saw this. The bottom ones were replaced but not the top ones. I imagine it was because they were faulty and not the top ones, perhaps someone wanted to pratice on this mobo (who knows). Although it has only 107 days of use.
He bought it already jailbroken and modified. The tantlum mod and a Western Digital 250gb HDD, but the person who did it was lazy enough to not repaste it or change the coin battery. It was pretty clean tho, so I was able to drag down the temperature by 8 degrees Celsius, almost 15 degrees Fahrenheit by only applying fresh Arctic MX-4 thermal paste.