A tricky problem!
We operate a Schiebe Falke SF25C motor glider, recently the canopy was replaced and the framework required welding. Since then the wet compass has been useless- impossible to swing and gives errors in excess of 50 degrees! We suspected that the canopy frame had become magnetised during the welding process and we tried to de-gauss it using a television de gausser - to no avail.
Anyone out there with any sensible ideas on how to cure this problem?