Optical Engine in a Mits WD-52527

My parents have a WD52527 and the picture has gotten darker over time. They are relatively heavy smokers and that's likely the problem. We've cleaned the mirror and the lens (the one immediately before the mirror) several times and it helps but the picture has gotten progressively darker. A new bulb didn't make a difference.

Does anyone know if the light engine is sealed to prevent smoke from entering?

If it's not sealed, its optics are probably coated with smoke. Does anyone know if it's possible to disassemble and clean the lenses, mirrors and LCD panels?

Is the light engine available as a replacement part? I haven't been able to find it on the net. The part number is:
938P015010

Thanks in advance