The FC on my Gitane loosened up on a ride some time back, I put Loctite on it and has remained fixed. I can't remember which variety of Loctite I used but it did the job.
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1971 Paramount P-13 Chrome
1973 Paramount P-15 Opaque Blue
1974 Raleigh Professional Blue Mink
1991 Waterford Paramount
Holland Titanium Dura Ace Group
Holland Titanium Ultegra Triple Group