It seem that my trusted GT31 GPS is now struggling with the week role over (happens every 19.7 years?) and it now thinks that it is year 2003. Is there any way to fix this?

try updating firmware?
The GT31 should be getting time info from the GPS satellites. Have you had it turned on in the open lately?

As far as I know the only input you have to time, is your time zone. There's no way to change the year.

My GW60 forgot the year when it was indoors for a few months.

I wrote a simple python program that adjust the date in .sbp files. It can be used for the GT11 / GT31 which suffer from the gps week rollover problem : github.com/RP6conrad/GT11_gps_week_rollover
A windows executable is on github, for Mac / Linux, you have to install python and run the python sketch.

Nice script, does it also works with .SBN files ? This is the default format i believe for the GT-31...

Can you send me a sbn file (pm), I will check it out.
Greetings, Jan.

Thnx, you got a PB