I have a 1mm spacer between the mavic lockring and a standard eai cog, both have never slipped. A few years ago, I had an eai cog and "standard" lockring on the other side of the hub, not knowing I needed the mavic lockring. Can't remember if I used a spacer or not. It was hard to tighten that lockring, but it didn't slip and the cog stayed tight. Once I found out about the mavic lockring, I have only used the "good" side of the hub, with no problems. Not sure if a mavic lockring would thread all the way onto the "bad" side now. My main issue w/ the rear ellipse wheel is getting the hub adjusted right, there is either slight play in it, or it's too tight. I run it with very slight play.
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1989 Schwinn Paramount OS
1980 Mclean/Silk Hope Sport Touring
1983 Bianchi pista
1976 Fuji Feather track
1979 raleigh track
"I've consulted my sources and I'm pretty sure your derailleur does not exist"