I too had a problem with an old RL70 (mono display) and initially sent it to some firm advertising on eBay who claimed to carry out repairs. They said that the Printed Circuit Boards inside were all corroded due to water ingress and that it was not repairable. They sent it back along with their invoice. The screws securing the two halves that would have to have been removed for them to see the internals had not been moved, so they could not possibly have seen the PCBs, so I queried their invoice and got my money back. I then sent it to Raymarine who fitted a secondhand screen from a salvaged plotter as that one was no longer in production, and it continued to work perfectly until I upgraded to a colour plotter and gave the old one away. Raymarines charges were fair, they fixed the problem instead of giving up, and there was no mention of any corrosion on the PCBs.