Several points. R7 provides the stop that prevents the lever from moving forward more than parallel to the DT. It also provides the base against which everything else sits. R6 is a friction washer, meaning it is intended to slip without wearing. If you replace it you should try to find a similar material. I'm not sure of the wisdom of putting Loctite on the threads. The screw is meant to be movable, after all.

All of which is to say you haven't really solved the problem, you've just covered it up. The real problem is the stem mount that apparently isn't appropriate for those levers (which some mechanical engineer at Campagnolo spent hours, or perhaps minutes, designing). In any case, those of us who have ridden for a while might recommend that you try DT shifters anyway for several reasons - they give a more direct connection to the derailleur by having one less housing section, and the supposed advantage of stem shifters isn't real, they aren't easier to shift or to reach and they don't let you stay balanced on the bike any better. Really.

As for the FW, there is no visible wear on those cogs. They show practically no use at all. Another FW, let alone a NOS one, would be wasting money IMHO. Perhaps the chain line is really bad. Under what conditions does slipping occur? What chainring and cog combination? How high is your cadence, are you mashing or spinning?