I owned an LS-3 for many years, which has the same water ballast
system, I believe. [I was also a moderately willing participant in
Erik's "nightmare" job on his LS-4 ].

I've heard from other LS owners that the little rubber boot that seals
the valve pushrod where it enters the valve body can leak, either from
a crack or hole in the boot or from loose clamps at either end of the
boot. The difficult part of any work is getting the valve assembly out
of the wing. I can't recall the specifics but if you've had the bags
out of the wing, you've already conquered loosening the big nut that
secures the bag/dump tubing to the valve. The rest of the difficulty is
working nearly blind through the hole in the root rib to remove the
valve. No cutting required, just long skinny arms with powerful
fingers. I know the factory had at least one special tool (a
long-handled wrench to loosen/tighten the aforesaid nut) and there may
have been others.

One question I would ask is whether the leak occurs anytime water is in
the tank or only during filling/dumping? Is it better/worse when the
left wing is up/down/level? Etc. This could help indicate where in the
system is the leak.

Chip Bearden
"JB" ASW 24