Always start with optics cleaning, then see if you still need to change the fluid.
On Philips beware of the deeper optics cleaning, because to get in there to do that on the sets I've cleaned you necessarily have to release fluid, or at least break the seal of the coolant chamber.
Whether your set needs the coolant changed or not is best determined by removing the screen and looking straight down into the lenses. As far as optics cleaning goes, any set over 1 year old will need optics cleaning, it needs to be done on a yearly basis if you want your set looking new - as in fresh out of the box - at all times.
Removing the screen for optics cleaning purposes gets you in there anyway, so it's an easy observation once you're in.
Contact me if you want from the shoulder guidance on doing the optics cleaning completely and yet still safely. Lenses are made of very soft plastic that is easily scratched - which is instant and permanent damage - and the mirrors of all rear projected HDready displays will be front surface. Mylar is incredibly fragile and instantly scratched, and you don't want to be mixing aluminum with ammonia on front surface glass mirrors. Chances are you won't be cleaning any glass surfaces in there at all, which is the only surface hard enough to not sustain possible damage from regular cleaning methods.
Contact directly me if you want my experience on the case with your set.
Edited by Mr Bob - 12/25/12 at 9:13am