Martin;
Re your gearbox, I hope this doesn't happen to to you, and maybe it won't if the salt water was only in there for a few days. However, mine went undetected for a couple of months, by which time the corrosion caused slipping of the forward cone clutch. I was unaware of the cause, and mucked around for months trying to diagnose it before finally sucumbing and pulling out the box. I disassembled it at home and cleaned up the cone surfaces, which despite my fears was a pretty straightforward job. Probably took me a day and a half all up, but if/when I do it again, I'd be able to nail it in a day. I'll probably have to eventually as it has a bit of bearing noise, and a slight leak if run for more than a few hours. Not surprising given the corrosion.
PM me if you need more info.
Cheers, Graeme