POR15 makes for a great glue. If you remove the top of a can and pour out
some product, the groove where the lid meets the can cannot be cleaned
enough to ever get that top off again. What people do is to either buy the
POR15 in the very small cans, or punch holes in the lid and use sheet
metal screws to plug the holes.I do both. I like the small cans, and if
you consider the waste from buying large cans that get the lids glued on,
they are a good buy. The small cans are far less messy to work with.

Thin your POR15 5 or 10 percent with their thinner. This will give you  a
much better final finish,than if you brush it straight. POR15 says that
the product leaves no brush marks. This may be true, but the finish is
uneven when brushed. Looks less than what you exected, unless used on very
small parts. Their thinner is Zylene based.Dont expect to reuse your
brushes ,unless cleaned with this thinner.The thinner is so expensive that
you will usually throw your brushes out.Brushes can be cleaned of POR15
chassis black and sterling silver,using mineral spirits.

I believe it will help your metal ,even if painted over paint. Regular
paint drys by releasing a thinner into the air. A web like structure
remains on the object.Moisture gets in.POR15 drys by absorbing moisture
from the air.It drys quickly ,here on  the easty coast. That is a good
reason to use a thinner in the POR15.This will allow the brush markes to
blend before it drys.A completely different animal,it is. This microscopic
cross section has no web,and will block moisture.Just put it on so it
looks good.