It is hard to tell, but that looks like a shunt. Do you have an ammeter or SOC indicator somewhere aboard?

I would extend the wires, and move the device from this location.

 

Looking at the picture again, I suppose that could also be your boat's DC negative bus. It is hard to say from that pic... (It would be AWESOME if everybody stopped embedding pictures into posts and, instead, linked to images hosted elsewhere)

Remove and replace with a BusBar and adhesive lined heat shrink crimp connectors.

 

The part that is is shown with a screw is something that can move up or down when the screw is lose and a wire can be inserted under. The bar shown is the ground for the connections.
Maybe the easiest way would be to mechanically remove the 2 bad parts, drill a hole and thread and replace with a screw for connection.
Thanks,
Charles

 

Are those solid conductors? The attachment looks like something you would find in a residential panel. Go with Eherlihy's suggestion that's some pretty work there. Solid conductors are BAD if they are, if not probably the wrong connector or at least one you need to look at real good. I have a lot of spades in my panel, I don't like them, I will go with a bar like E posted when I do a complete rewire, for now I replaced probably 1/3 of the spades because they would pull right off or not crimped right.

 

These are regular stranded marine wires. This boat was built in Sweden and I suspect that these sliders are going to be very difficult to find.
Thanks,
Charles

 

Most times even if the end looks bad, strip back a little and you're good to go. I spent the money on a good ratchet crimper its worth it in quality connections. Lifetime tool too!

 

You can find them in the US they are an industrial style common in Europe. They do slide off so you would find the end of the bus bar typically supported by plastic held in with a screw. Not sure what brand you have there. We have some in the shop similar made by Phoenix.
These are the type we use thou at a glance it looks like yours may be a different brand.
Phoenix Contact - 0404017 - 7 mm W 41 A Silver 20-10 AWG Screw Busbar Connecting Term Blk Conn - Allied Electronics

 

I suspect that if you first use a Scotchbrite pad, as best you can, or a Dremel tool with a wire ball, to remove whatever corrosion you can, and they spray the rest with PBlaster (not WD-40) you will find a lot of the corrosion goes away. PBlaster can be used, left 1/2 hour repeated two more times, and all sorts of rusted parts come apart literally as if they were new bare metal. There are other similar products like Kroil, but PBlaster is the one you'll find in retail stores. Even the big box stores now.

 

I did that on one of them but used some "totalboat" rust inhibitor and it should be ok. The other is gone too far but thanks to Colin link above, I was able to locate some of these parts.
Thank you all for the advises,
Charles