Here's an update from me. I finally called the company this morning. (Note: despite the fact that they proudly announce on their website that they listen to every voice mail and read every email, there is nowhere on the site that lists a phone number. I had to do an internet search to find them. They also have no email address, but the rep this morning told me they do have a form to fill out somewhere. However, that's really not obvious even on the "support" page.)
Anyway, when I finally reached someone, she was adversarial from the beginning, bordering on argumentative. Decidedly unhelpful in "feel" even though naturally her job is to weed out issues before people send in the units. Or maybe she was just having a bad day.
At any rate, it seems the only way it can be dealt with under warranty is to send the units back. I suppose if we did that we might get a replacement - but as the rep pointed out, to have this issue arise only after 5 months is fairly unusual.
So we've decided to keep everything as is, save our postage, and ignore the rain gauge.
I won't ever be buying a La Crosse product again, though.
Kathy