The GPS engine needs to be replaced in the GPS Nav. Cambridge will
perform that and provide a fresh calibration/cetification on the unit
for $350. I would have them recalibrate the L-Nav flow sensors for
variometer and airspeed as well to put the L-Nav in new condition -
they'll do that for $75.

I'll let the lot go for $1100 and throw in the battery charger - and
I'll pay the shipping.