I've heard about both, never used either. I'm looking to prevent galvanic corrosion between stainless fittings mounted on aluminum masts and crossbars. Anyone have first hand experience with either of these? The lanocote is about $12 for 4 ounces, tef-gel is $12 for a 1/4 ounce, so quite a price difference.
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I've used both and I like and use the Tefgel.
Example, I installed a couple spinlocks low on a mast three years ago with #10 machine screws. It's used a lot in salt water only. Recently I removed the mast base to mess with something else and I had to remove the spinlocks. There was zero corrosion at the mounting holes. You could also see where the Tefgel had soaked into the aluminum about a 1/4" out from the holes.
When you put larger fittings on a mast put electrical tape on the back of the fitting first to help insulate it from the mast.