Redbull661, Thanks to you and the other testers we were able to develop a superior filter kit for the 661. Part of the secret was a better fitting cover that distributes the airflow around the filter element so that it doesn't allow spotty buildup areas. As you have demonstrated here, it is important to use a good quality
foam filter oil (no bar lube, motor oil or gauze filter oil!) to get optimal efficiency and long run times. While we can't promise 25 tanks, testing has shown significant run times over stock, while holding new filter power levels.
We would recommend
cleaning the element before any debris gets through, as you know, it is the oil that traps the fines. Find a cleaning interval that works for you. When I was working years ago with a 064 I carried a couple of extra elements in a plastic and changed them out every couple of days whether they needed it or not. Then when I did my weekend saw maintenance I would wash, dry, oil and bag them all for the next weeks run.