OK problem of water ponding in the channel of the sliding door is solved.

I checked with the people who did the rust protection.  Apparantly surplus
rust protection liquid drains out of the drain holes where they inject it
and collects in the channel.  I guess it collects unevenly causing water to
pond there.  It is a rather waxy material and the depth of water over it
probably looked more than it really was. I was told the protective material
will become more liquid in warmer weather and also drain away from the
channel leaving behind a thin protective film. It can apparantly be removed
with solvent, but I was advised to leave it.

Barry