I am a bit late on this post but I thought I would add my 2 cents worth. It goes against what most posters say but hey....
I think it is a good idea to replace the thermal past. I would never trust factory compound. I use Arctic Silver 5 (AS5). I does not run. I have used it for a long time on MM's and my MacBook Airs. It has never run for me. See also their website on this comment.
Also it is not as conductive as people say. There are
postings on the internet I have seen that say this is a rumour. I have seen some posts on doing ohms testing on AS5 with the result being zero. Right or wrong I don't really know as I am not technically minded in that regard but the AS5 website says it is not conductive. Having said that I would not want it touching anything other than the edge of the contact surfaces anyway.
A point to note on the late 2012 i7 2.6ghz (bought in March 2013) though which I noticed is that there is a very fine gap (super fine) in between the heat sink and the surface of the 'square' processor (I assume GPU), while the 'rectangle' processor (I assume CPU) sits almost flush against the sink. I noticed this when I put AS5 on and had a look with a small led pin light under the sink and noticed I have put too little paste on the square GPU processor. You could see that it had not spread to the edge of the square processor surface. You cannot bend the sink or do anything because there are little stainless steel spacers that keep the sink at the exact level so it does not appear to be a flaw. The spring loaded screws keep the sink sitting on the spacers perfectly. What that means is that you seem to need a little more paste on the GPU square processor to account for the slight space. I put about two rice (short grain) beads of AS5, while I put a thin strip (1.5mm wide) of AS5 on the rectangle CPU. After close inspection with the second go the coverage is perfect. I note AS5 is put on differently (not spread) to some pastes which you spread flat. See the AS5 website for instructions.
Having said all that you can use your choice of paste. All I am saying is have a close look first to see if you have the space like me.
I think the space exist due to simple geometry in that you have about 4 or 5 spacers keeping the sink at an exact level and two processors underneath with the chance of the sink sitting exactly on all 6-7 points being minimal in chance.
Also I use the exact stand philipma is referring to above. It works wonders and takes up less space (and keeps the bottom black cover scratch free.
Having said all that, the OP's temps are fine. I had the last mm 2011 2.0ghz quad and it ran those higher temps when I pushed it with say handbrake (which I use for a few days straight many times). It is still sweet two years on.
Watch this space... Sorry bad attempt at a joke.
IP