Nice to see that you got your PB100 up and running - nice little machines and so easy to pull apart. I had a similar issue with a PB100 - exactly the same distribution of marks but yellow; it slowly grew and became worse, which made me think it was some kind of algae growth. Nice to see a Mac can support both organic and inorganic matter Unless you feel adventurous and strip down the screen (if you have nothing to lose), I'd look out for a dead PB100 with good screen and do the switch one day.

JB