Hello.I have a ps3 40gb model working with no problems for over two years.I changed the thermal compound every year and do some cleaning.Is it really neccesary to remove the rsx heatspreader and reapply adhesive on the vrams and paste on the actual chip.I never changed the paste below the rsx but its been almost three years and Im wondering should I do it.My philosophy is that no matter what paste you put on the heatspreader it doesnt matter if the paste below the heatspreader is dry and old.

If I remember well... all heatspreaders used on big chips (AMD CPU for example) who have thermal issues (that's why they use heatspread) don't use normal thermal paste between the die and the heatspread. They use like a very thin sticker and you can't replace it.
The idea of the use of heatspread is to transfer heat as spreaded as possible to the main heatsink. That ensure that the heat is not focused over the chip die all the time but spreads to larger surface to enable the cooling to be more effective keeping the temps low enough.
So, if you ask me, just don't bother with it.

This is incorrect with regards to PS3, if you remove the IHS from the GPU and CPU you will see it is just normal thermal paste and it's usually dry enough to just wipe away!

Changing it can make a HUGE difference. One console I reballed yesterday came back to life after YLoD, but it would overheat within 30 seconds or so. I replaced the thermal paste under both IHS (had already replaced the heatsink stuff) and now it's been running for over 6 hours with no signs of overheating. Replacing it does make a BIG difference!

To remove the IHS from the GPU, first heat it up to approx 150*C, then just "pop" it off using a BLUNT instrument. Go in through the hole from the CPU side, because there is nothing there to break. The other 3 sides have capacitors which can be broken.

To remove the CPU IHS is considerably more dangerous and much easier to damage parts. You need to use a scraper tool that takes single sided razor blades to cut through the silicon holding it down. A youtube vid is here... http://www.youtube.com/watch?v=6xZ0PUsAWlM

Not a great vid, but the guy shows you the jist of it and the only one I could find for CPU IHS removal.

NOTE: after removing the IHS on the CPU and GPU they will not make contact if you only apply a thin layer of thermal paste. I find it works best to apply a thin layer to the die on the chip, then an "x" onto the bottom of the IHS, but only in the area where the die touches the IHS. Then place the IHS on the CPU/GPU and move it about a bit to spread it over. Sometimes its worth popping it back off just to make sure full contact is being made and both the under side of the IHS & the die have thermal paste on them after spreading.

Oh, and this is what COULD happen if you don't use heat when removing the RSX IHS....