For anyone running your 5411 in salt water, there is a good chance that the cooling passages are clogged with scale. Time for an acid flush. I have had to do that on my 25 year old 5411 several times. Oxalic acid from the hardware store circulated with a portable
pump will safely and quickly dissolve the scale buildup. Vinegar isn't strong enough. Don't forget to remove the thermostat to permit free circulation and avoid possible damage to the thermostat.