The GPS on Blue Opal has been failing recently, claiming that it can’t get a fix. The common answer in the forums is that the battery has died, and should be replaced – spot welding the tabs will be the hard bit, but doable. So, I took mine off the railing, and discovered that it really wasn’t a happy bunny.
The top plastic cover was cracked, and all the threads were seized. Snipped the NMEA cable (I’ve got plenty of length, and can do a splice in the lazarette to fix it back), took it below, and went at it with the rubber wrenches. No dice. Cracked the plastic mushroom right off, figuring I can replace it somehow, and found that every single thread was totally seized.
Cleaned off the crap, popped off the lid, and concluded that I need a new one.
Corrosion 
More corrosion 
Is that rust I spy on the contacts? 
That’s definitely rust on the circuit board 
That bit’s not looking too bad
There were salt deposits inside the unit, the board has rusted, and the battery is putting out 2.9V.