I also like to vacuum test the multi line connector that goes into the fender. Test it from both sides of the connector. Occasionally you'll find a small leak there. I've started watching it for some time, and have had to replace two of the lines. They get dried at the end and can crack open. You know you have the best seal when you get in your truck after it sits for a day, and there is still enough vacuum to move the mode door.
