On Monday, March 22, 2021 at 7:37:22 AM UTC-5, trader_4 wrote:
On Sunday, March 21, 2021 at 11:12:43 PM UTC-4, wrote:

Why not treat it like any other straight thread fitting and put a
gasket under the lock nut. That is what Yamaha does on their
outboards. An O ring that is tight on the threads should work.
I don't see how a gasket or o-ring under a lock nut keeps water from
following the threads, right on through the nut. I've never seen a fitting
that worked that way. Gaskets work where you just have two flat surfaces
meeting. It would work with a *bolt*, because it's a bolt, not a nut and yc
the bolt doesn't have threads coming out the head to leak. The washer
will seal the perimeter, but do not the path through the threads.

Hydraulic fittings on farm equipment sometimes use washers with O rings or flat rubber
washers at least on the low pressure return lines. The washers are made with the O rings/rubber washers
attached. I think the washers are convex and collapse as one tightens them so the O/washer collapses
against the fitting as things are tightened. This might be a good illustration.
https://lenzinc.com/sites/default/files/AAL_1.jpg.
Maybe your local hardware or auto parts store?