The problem is /was that the LCD mountings are not marine robust, and fail after about a year.
Northstar have bought Navman range and have retooled the LCD mounting. The issue of condensation will remian though.
My 3100 Repeater is the only one to have survived for 3 years without failure, most likely as it is mounted on the main instrument panel by the chart table, all nice,warm and dry.
Should be some stock of those left. Try Navimo on 01489 778850.
I've got a full suite of Navman / Northstar products, including the 6KW digital radar, 12" and 8" colour plotters / GPS, sounders, AIS, VHF, fuel flow sensors etc and I must admit, they've all been excellent for performance and reliability.
Several people I know have the small independent GPS / Plotters and they've been OK as far as I know. Maybe the earlier Navman products were not so good, but modern ones seem to be OK.