BillV wrote:
snip
The mold you get on silicone sealant seems to be embedded within it.
My theory is that its the acetic acid thats used to cure it going moldy.

Nope.
The acetic acid is gone after it cures.
When you stop smelling vinegar, it's gone.

It extremely difficult/impossible to remove if this is the case.
You could try silicone eater but I've had limited sucess with that.

Its down to hard work with lots of scraping and cutting.

A nice sharp scraper makes it not too bad at all.