1 - I was confusing cannister with filter. I'll re-measure.
2 - The filter length DOES directly affect o-ring. Look at Anton's diagram. The filter presses against the black square o-ring which presses against the cover. If the filter is too long, this moves the cover outward which effectively reduces the pressure (or increases the opening) for the white o-ring.
3 - My white O-ring appears unblemished when I took it out, so even if I measured wrong, i'm close to the danger zone.
4 - What is the procedure for the "remove cannister and put shim BEHIND it" mod?
Anton, thanks again for the great website. I didn't see that article before (seems a trend, no?).
Joerg. Forgot your tips and tricks blurb. Pretty much sums it up.