Update. When I broke my display again I used the opportunity and drilled a hole in the backcover, allowing me to attatch different antennas to the gps antenna connector. That brought no good results, but it ruined the backcover. So I used the old backcover again, but this time I took the PCB off as well and applied conducting silver to the point where the PCB touches the contact bridge in the display part, and after refitting the PCB I applied conducting silver to the point where the contact bridge touches the wire mesh in the backcover. Gps has been wonderful since then. So I dont think that the gps antenna in the backcover degrades, I guess that just the two contact points leading the signal from the antenna to the PCB are corroding.