"autonut843" writes:

Don't try this until someone else gives their thoughts on it.
What if you pressure washed the outside with a mild bleach solution?
If the water already was able to get there, then the bleach solution
may be able to get to the same places that the moisture that caused the
mold got to and whiten it up.
Does anybody see any problems with this solution?

Ever use a pressure washer?

Do you really want to get bleach everywhere?

Sorry, no opinion about the OPs problem.