If it looks like the instrument cluster has been changed out on it, I wouldn't trust the miles. You may be getting into a lot more than you bargained for. I would get a compression test done.

At this point just about any SL from the 80's that has been a daily driver is going to have been repainted at least once. I bet the re-paint job is peeling - body shop applied paint usually sticks better on the horizontal surfaces than the vertical.