I notice that most US web-based vendors who used to carry the original
Lifesling now list it as no longer available.

They instead list a cheaper "Lifesling 2."

The new version replaces the (USCG-approved) original's 150' of
polypropylene line with 125' of unspecified "monofiliment."

Has anyone here ever tried to use this stuff (monofiliment) on a
winch?

Al
s/v Persephone