Chuck,
I did a new construction job a few weeks ago where the mud left that red stain on white paint. Tried really hard to get it off but couldn't. Fortunately, I was prepping the job for the painters to do their final work. I saw the painters at the site the next day and one of them said he'd been painting for 30 years and had never seen anything that would clean it off.
Maybe someone on this board will let us in on their secret on how to clean it! IF anybody can actually clean it off.