Prius (2004-09) :: GPS Keeps Deleting Track Of Previous Destinations

Bought a used 2007 Gen II in 2009, and have since that time been very happy and had few issues. However, lately I have noticed some problems that are very disruptive, and am concerned they may be indicating a bigger issue ahead.

I rely very heavily on the GPS, using it every time I drive. In the past few months, I have noticed that sometimes when I start the car, all of my "Previous Destinations" have completely disappeared, and it says "no previous destinations"! Which is insane, because I have been accumulating previous destinations for 6 years now! It is hugely disruptive for me to find these gone, because I reuse many a few times but don't want to save all of them to "My Places." Strangely, My Places are still there, not deleted. The deleted destinations never come back, and I have to painstakingly enter all my addresses again, which is difficult for me because of a disability. In the past few months, this has happened 3 or 4 times! When this happens, the region is also always reselected to zone 9, which I am not in (not sure if that's where the first owner lived?), so I always have to enter everything in all over again.

A few years ago I had to replace the 12V battery, and I can understand why I lost all my memory in that instance. But the battery should be fine.

I have also noticed a few other strange occurrences in the past few months, which may or may not be related. There are times when suddenly the key fob does not work, and I cannot get into the car. The battery is new, so it's not that. I was worried it might indicate an electrical problem, because also a few times now I have gone to start the car and it goes into battery mode instead of turning over - as in, the indicators and lights come up, but the car doesn't start. Fortunately, when I turn it off and start again it has resolved. A few other times, I have started the car and the buttons seem to be crossed - pressing Destination leads to Audio, pressing Menu leads to Map, etc. Again, fortunately I restarted the car and all buttons worked normally again. Same thing, once I started the car and the screen did not turn on at all, just stayed black. Restarted, and it was back on.

So I am wondering what these sudden destination deletions might mean in this context. I am very far away from a dealership, and can't afford a major work-up if it's not necessary. A few possibilities I considered are that the destination cache might zero out when I have not used the car for an extended period. I don't drive every day, and there are some times when I don't use the car for 2 weeks or a little more. I also live in a location by the ocean, and so I have wondered if perhaps the salt air is corroding my electronics. I have tried to rinse the underside of the cab with fresh water every few weeks, but other than that I don't know what I could do to prevent salt damage.

Maybe what's going on with the NAV is totally unrelated to these things, and can be solved simply in another way. I have no clue really what's going on. But I don't want to have to deal with this again. And, if there is reason to think a serious electrical or other problem might be imminent, I would like to know that so I can take care of it before the car gets totaled, because I'd really like to keep my Prius for a long time if I could!