As far as I know the ZS1 was a joint venture between Zander and SDI from the start, so basically it still has full support from SDI. In any case, a fix is available from SDI. They replace the lithium batterie of the GPS module and make some software changes to the Garmin software. When returning the Logger it is also recommended to have the internal lithium battery replaced since it is usually well along the path of it's ten year lifetime.

I paid around 180 EUR for the fix and the internal battery replacement.

Since you need the GP941 to provide a GPS signal to the ZS1, reverting to a more modern logger is not really an option unless you want to replace the complete setup.

As an alternative an NMEA input mod is available for the ZS1 which will allow and NMEA source to be used to feed a GPS Signal - even though that will probably cost similar effort to having the logger fixed.