Mfine

My gps often loses the position. The arrow wanders off, the screen rotates irrespective of the north arrow. Sometimes it freezes. Then it might come back, work fine for some time, then gets screwed up again. I had the system fitted with a switch wired to intercept the speed sensor to trick the system into thinking it is at a stop and allowing to quickly enter a destination. It has worked well until a few months ago. The system has a coupe-of-.years old DVD. Someone has suggested a new DVD might help, but I don't believe it. Two questions:
1. Has anyone experienced anything like this and found a fix?
2. Does anyone know a good electronics tech in LA area who could troubleshoot the system?

Thx.