The GP-39 is available here in Australia from a number of chandlers.
Some big differences to GP-90 - it's a lot smaller, so you'll need to reduce the size of the hole, and it has only one NMEA0183 port and one USB port so you'll have to reconfigure how you send the GPS signal to the devices your GP-90 is connected to.
I'm curious about this date rollover issue.
According to Furuno, a cold start will reset the device and the position information will be correct, but it will display the wrong date.
Correct me if I'm wrong anyone, but I don't think the date is actually used by anything my GP-90 GPS is connected to.
UTC is contained in some NMEA0183 sentences, RMB for example, but is this calculated in the Furuno, or does it come from the satellites?
I don't know the answer to that and I can't get to the boat to see what effect this wrong date has.