Hmmm.
Mine had vertical lines on it (like, really bad ones) a number of years ago, not long after I had the WAAS upgrade done, then it stopped, and has not done it since.
Garmin has a flat-rate repair which is pretty much a, "jack it up and drive a new one in" deal. Assuming it hasn't been, like, flooded. And isn't a 28v-only unit (which they no longer support). Around a grand, which seems pretty reasonable in today's pretend money.
I say, watch it and be ready to ship off for rework if it gets worse.