Daidnik could be right. But when I reassembled my steering wheel after making the same repair, I found that the horn ring has tabs on the back that must fit into slots in the hub assembly. If they aren't lined-up when the wheel goes on, the ring sits too proud. I noticed it because the chrome horn thingy that you push had no movement when I first put on the wheel.

Just saw your next post. On my w110 there was a washer behind the plate as well as one in front. I believe that your assembly is essentially the same. The snap rings (there are 2) are actually pretty large and a standard set of snap ring pliers should work. It was a little tricky getting the last one seated into its groove.

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1981 300TD 310k miles
1970 280sel 172k miles
1966 230 Fintail 162k miles

"Where are we going? And why am I in this hand basket?"