Capillary action of fluids down the inside of a wire is not unknown (Discovery 2 TD5's suffer with engine oil migrating down the loom and into the ECU
), but the distance involved in this scenario on a 75 is much greater.
As salt water would cause corrosion of the copper, I'd of thought that we'd be seeing problems of the wiring corroding away near the fuse box, long before the miniscule amounts that would make their way to the LSM, would cause any overheating ?