If your Nav VI is duff, contact garmin, they have just changed a mates that is 5 years out of warranty for free. My replacement cost me £150. Looks like garmin are now stepping up
I cured mine.
I found that the screen ghosting only occurred when the battery needed charging.
I take the nav into the house and day before a ride i charge it up on the plug, so when it goes on the bike its fully charged.
Of course if you use you bike everyday then it should be charged.
Mine has been behaving itself for over 12 months now.
so for me at least that was the problem.