Interesting, apparently this is a flaw that has crept into a lot of production rifles. I recently bought a No. 1S .30-06 and it does the same thing, the tab that holds the lever shut isn't tight so you can jiggle the lever ever so slightly up and down.
I might have to call Ruger to see what their suggestion is.
My guess is they'll say it's "within spec", the catch-all phrase that's all the rage with gunmakers these days. My brother's trick worked well and was invisible. A fussier person could use metal and solder it in I suppose (he was fussy enough to have a pristine Kimber of Oregon .22 and a couple of nice double guns rust-blued, but whatever). As long as it doesn't rattle just from movement, I don't much care, but it's another, albeit minor reason I somewhat prefer the 1885s to the Rugers, even though I own both.