A temporary fix.
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The only strap that I have found to be truly safe for over-the-shoulder carrying of a camera is the Upstrap and the reasons are simple. First it has deep nubbins on both sides of the rubber shoulder pad and for over-the-shoulder carrying that’s essential as the strap will always twist in practice. And every other strap out there appears to have a rubberized side and a slick side. Once the slick side is in contact with your shoulder the whole ensemble is nothing more than an accident waiting to happen. Second the embossed maker’s name is invisible.
The stock strap for the Leica fails in three respects. It has only one rubberized side and they spared the rubber. The other side is as slick as it gets. Duh! And there’s objectionable and loud “LEICA” stitching which helps your neighborhood thief make a beeline for you.
I keep searching for a second Upstrap on eBay but so far without luck. My M10 sports the slimmer version for lighter cameras and it works superbly.
So while I wait for one to crop up I have enhanced the design of the stock SL2-S strap and made it far les slippery using some leather patch and non-slip rug pad gripper.

The nubbins are more pronounced on one side.
These should be placed to the outside of the strap.

A two inch wide strip is cut.

A six inch long and two inch wide strip of leather patch is cut.

The anti-slip material is wound around the strap and the leather patch
applied either end to secure it, avoid damage the original strap.
Pretty? No. Effective? Yes.