I found some DOT compatible grease meant for assembly of internal lever body and caliper parts of Avid hydraulic disc brakes for bicycles. DOT 3 is DOT 3, same fluid for a car or a bike. So I bought the last two tub of it that my parts vendor had. It's a soft kinda like lotion consistency grease, the closest analog to the little capsule of assembly lube that used to come in NAPA wheel cylinder kits way back when.
It's meant to control rust and corrosion on mountain bike brakes, a particularly muddy and moist environment, so I don't see why it won't work on a wheel cylinder too.
