Regarding the erratic meter needle swings, it may be that a simple cleaning of the ring resistor may be sufficient. Especially if the camera has not been used for a while. This part is located inside the black DP1 meter housing and looks like this:

Full view

Detail view

It's those tiny little metallic bands that pick up the gunk over time. I had the ring resistor in an identical DP1 cleaned years ago and it continues to work perfectly to this day. It's not a big deal to have this done.

Beautiful camera. Excellent price. Good luck with your sale.