For those of us who work on marine engines that are used in saltwater, we face extra challenges due to the corrosive nature of the environment. Unlike our freshwater brethren, to remove a fastener we cannot easily break a bolt loose with a wrench then unscrew it with our fingers. In coastal regions, mechanics and DIY types have to allow for extra repair time spent attempting to remove salt-frozen nuts and bolts. Sometimes one has to drill out screws and re-tap or Heli-coil the damaged threads.
Experienced techs often use a marine grease or an anti-seize product to keep bolts from becoming corroded or stuck in place so future removal is much easier. Grease often washes away if it's not a good marine rated lubricant or it may melt from the engine heat with seepage down the outside finish of an outboard. An automotive brand of anti-seize paste may contain copper ingredients which cause a galvanic reaction when used on aluminum components found in outboard motors.
Galvanic corrosion, erroneously called electrolysis, occurs when dissimilar metals are in contact with an electrolyte such as saltwater. Copper in contact with aluminum form a battery if seawater is present. Stainless steel bolts will do the same but less aggressively than copper. Electrons flow from the aluminum causing it to erode and form pits or holes in the metal. Over time this can eat away threaded areas allowing bolts to loosen and perhaps fall out. Other times cavities or pits could form in the surrounding areas. Either situation may cause a failure of an important component.
One company makes a relatively economical anti-seize product specifically for marine use that is organic. Jet-Lube, Inc. of Houston, Texas (www.jetlube.com) offers large and small containers of their metallic-free marine grade of anti-seize which protects up to 2400°F and is non-conductive. It is not considered a marine pollutant and is highly water resistant yet meets the military MIL-PRF-907E specifications. Being a thick dark-colored paste, it does not stain items with a silver gray coating that common anti-seize products do which smears onto tools, hands, and boat parts. Very little Jet-Lube compound is needed to protect threaded parts and a brush built into the cap makes application clean and easy.
You can find Jet-Lube Marine Anti-Seize Paste online at Amazon.com or through industrial supply warehouses. Another good thing is that it is priced several dollars less than some other brands, about $12.95 for ½ pound. Every saltwater mechanic should have a marine approved anti-seize in their toolbox.