It is a must that this PS3 gets service, strip it right down get everything out and clean the whole lot, use cotton buds and spend 2 hours cleaning it. Use Isopropyl alcohol and clean the mobo and the heatsink. New AS 5 paste applied.
If it has a loud fan then you need to remove the IHS and change the thermal paste below the IHS. This is not for the novice though.
I buy and sell PS3's and its amazing just how bad some are, I bought one yesterday for just £30 which was listed as not reading games, when I got to the house to pick it up I thought oh my God I'm not even going in, those guys in the UK will know when I say Shameless what I mean. Any way got it to my home and I did not even take it in to my house it was that bad, I opened it up in my garden and then spent the next two hours cleaning every single part with alcohol and disinfectant. It was full of yellow goo and fluff in side. Smokers house and think peoples lungs are full of the same sh*t.
Cleaned the lens and guess what I now have a full working ps3 for £30 it never needed a new lens it just needed cleaning.