I did this job this weekend, and I cleaned the contact rings first with a paper towel to remove the surface gunk & then rubbed with a pencil eraser & then with q-tips tipped generously in alcohol. I also cleaned the four rectangular copper pieces & wiped & qtipped all the protruding contacts on the steering column to get them clean. Everything worked fine. BTW, before I did this my horn had not sounded right so I also adjusted/loosened the screws (30 torx) holding down the two long grey push-bars on the sides of the steering wheel, which were too tight The horn sounded just fine when I was done & the flickering SRS light was no more. My thanks again to Mike & the other forum participants for their helpful posts from last year.
BTW, to loosen the hex nut I got a long 10mm hex key from Sears ($4.20) & used the 5-inch hollow tire lug-nut extension bar which is in the MB supplied red tool pouch.