I don't think you'd want to run the washers that came with the eccentric bolts... OEM everything always kicks butt if you have the choice to run it as the factory intended. Regarding roughing up the upright, I don't think that would make much of a difference. Aluminum would deform and bite plenty fine at 100ftlbs x 2.
Is your torque wrench accurate? Are you sure it's slipping there? With 2x of those bolts torqued to 100ft*lbs you have around 12 tons of clamping force at those faces. If you aren't positive it's slipping there... I would recommend scribing a mark, and seeing if it slips. You may also want to consider ratchet strapping a 2x4 or large pry bar onto the wheel and getting a helper to try to yank on the suspension to see where it's shifting.
I hate to admit this publicly, but on the very first lemons car I built several years back (it was 100% a FAFO build), instead of using eccentric bolts, crash bolts, or slotting, we went to the closest hardware store, downsized to (I believe) 3/8-16, held max camber, and then torqued them to ~60ft*lbs. We ran the whole 15 hour race, had a few offs and one contact, and camber held the whole time. It was a bad idea... but it worked. To me, something else seems wrong if you're slipping there and torqued them. Does the strut slip on with a nice tight slip fit, or is it really loose? Perhaps the upright is too narrow/strut mount is too wide?
