Just re-united with my Z after 2-1/2 years and while checking the fluids I noticed the top cover on the plastic cap on my clutch master cylinder is separating from the side. It's about 1/3rd of the way off.

Is it dangerous to drive? Where can I get a replacement? Could I Super Glue it?

Check with your local auto parts store. In the "Help Me" section they sell replacement caps.