Jeff Liebermann wrote on Sun, 03 Mar 2013 10:03:27 -0800:

Thanks again. I'll spare you my lecture on the topic. The simple
version is from Sherlock Holmes, where Watson "sees" but does not
"observe". Plastic rot is similar in that we "see" mold, but few have
the time, abilities, and equipment to test if it's really mold.

Hi Jeff,
I think it's a rare combination of both intelligence, wit, and
inquisitiveness, plus the rarest of all desire to help others
to answer the question, that makes you so valuable for us.

A few on alt.home.repair have that quality - but not very many
(probably a half dozen, e.g., Oren, krw,