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I don't think Leica originally used Krazy Glue, but if rubber rings on some of their lenses are fairly tight and clean on inner side than there should be enough grip to prevent slippage when focussing.
Few months ago my Elmarit-R 28 started focussing past its hard stop, or so it appeared. That time I didn't even notice that unlike other R lenses Elmarit-R has rubber focussing ring instead of a metal one.
Making long story short, I sent it to Steve Camera Service Center (highly recommended, BTW) and they simply advised me that all they had to do is to re- cement/glue the rubber ring so it wont slip.
Michael is correct about being careful not to glue screws. Below is Summilux-R 80 with removed rubber band. I cleaned the inside of a rubber band, metal part around screws then simply applied 4-5 tiny drops of Krazy Glue every 2 cm and the focussing was perfect again without any slippage.
xenon99's situation may be different; however, this is what solved my problem.
And yes, it's beyond me why Leica (or Contax) would use rubber bands on some of their lenses!
Kudos to Zeiss for their current all metal Z* lenses.