Thanks everyone. I will pick up one of those little stirring units and then try again. I will let you know.
John - I'll add a bit more to the stirring benefit. My employer used polyurethane paint on it's fleet of commercial jets, being a hobbyist for many years and airbrushing frequently, I asked one of our techs about the paint type and use. He walked me to the paint storage room and showed me the cans, with very explicit printed instructions for preparation.
The instructions made quite clear the need for stirring before use, it stated specifically that shaking the can would not completely blend the entire contents, some of the settled solids will not come off the bottom without stirring. The paint would simply not perform as intended.
I used Vallejo Model Air for a while, their bottle instructions say to just roll the bottle between your hands to prepare for use. Once I figured out how to remove the little top dispenser and used the Tamiya metal stirring paddle, I was amazed at how much of the solids were still on the bottom after rolling and shaking the bottle, then forming a glob of thick material on the end of the paddle.
So, my personal discipline is to thoroughly stir any and all paints or primers, then blend with mixer and use the paint. Takes very little time and produces very predictable and consistent results. Just my thoughts, I hope this may be of use for others.