O-rings are not well suited to constant or high speed shaft rotation.. (by
high speed I mean motor shaft).

I worked on the Navy deep submersable program and we overhauled all of this
type of equipment.. There are seals available that are well suited for motor
shafts. A vendor that specializes in high pressure pumps will have something
for this job.

BTW.. The best way to deal with the compression forces in electrical cables
is to intentionally flood them with mineral oil in Tygone tubing. Just be
sure you purge all the air pockets by applying a vacuum before sealing the
ends. (old saying, "you can't compress a liquid"). This method works to the
deepest ocean depth.

--
My opinion and experience. FWIW

Steve
s/v Good Intentions