Where did you make your tap for the boost gauge? On my truck, I tapped the metal horn leading into the intake manifold. I would think it's impossible to clog up a boost gauge with K&N oil, unless you sprayed it directly up the boost line.
A more likely situation is that you've blown a hose, or have a kink in the boost line itself leading to the gauge. A more rare case would be a ruptured diaphgram in the gauge itself, but I think you could hear it hissing if you put your ear to it then.
Greg