When spray bombs don't spray??

[peteski]

From your list, acetone is the most "potent", although if the brake cleaner contains methylene chloride, that might be even better.     

[nkalanaga]

We use acetone at "the factory" to remove paint marker from parts, so it should clean a spray can.  It isn't plastic-friendly, so you might want to test it first if cleaning plastic-friendly paints.  Try it on a spray head from an empty can, just in case they used a plastic that doesn't like strong solvents.

I haven't had any trouble with Tamiya spray cans, or with Scalecoat.

[Joetrain59]

It looks like soaking overnight in acetone cleaned spray tips nicely. Even put some acetone in can neck where nozzle goes. Been busy with house closing today, and moving packed boxes to new place. Will try spray bombs in an hour or so.
 Joe D

 Got one can/tip combo working. Tried swithching tips and cans to see what culprit was, to no avail. Did see a lot of paint from tips in vessel with acetone. Have to use canned air yet. Will get mineral spirits later today.