Bob, you say you filled the USB compartment with the grease. That didn't interfere with the contact when you inserted the USB plug? Do you use it in the battery compartment?
That's the nice thing about dielectric grease, it doesn't interfere with electric connections, but protectes them from corrosion. I just wipe off any grease on the cable end after use and add a little back on the GPS USB socket before closing. I haven't put any on the battery terminals yet.
I'm surprised on how well the the batteries last. I'm only on my second set of AA's. I've never has a major moisture problem with the battery contacts in boating electronics, but I learned never to try to change batteries on or near the water. Too much moisture always got trapped in.
I keep most of my other electronics in waterproof bags, even if it's waterproof (marine radio) but more for quick cleanup. With the GPS, I haven't found a bag that will let me use it in the RAM holder.
It does seem that the salt and moisture get to everything, sooner or later though.
- - - - - Hobie Island Sailing since 2006 - - - - - 2011 & 2015 Hobie AIs and a 2012 TI