Another user denkiedenk has a different theory:
Completely by accident i left my pj running all night with the heating in the room fairly high ! (+- 28 degrees celsius inside). The weird thing is i noticed the pink line, wich had been there for several months already, DISSAPEARED ! about two weeks later it came back very slightly, so i decided to take a gambit, and used a blowdryer on the hottest setting and on low 'blowing' power, blowing gently hot air in the airintake, and oh yes, u could almost see the pink line dissapearing... since then it has never come back again....
I have tried this myself: I let the projector run all night with the lamp on High in a room warmer than average, and it seemed to me that the pink had disappeared (though the stripe itself was still there)
I'll check more thoroughly tonight