I'm in the same boat. It was real fun filling out my insurance and fsa forms when my planting data had wrong dates. No, I didn't plant corn in December at 2:00 am!

I did a search and found this thread here.  Also found in the user manual, "This display has an internal lithium coin cell battery that is good for the life of the product and does not need to be replaced."  Mine is a 2013, so apparently 7 years is the life of the device.

I have an inkling to do it myself, even if it were free to send it in, I'm no stranger to a soldering iron, but I might just put a label on the front to remind me to fix the clock every time I turn it on.  My GPS time button works.