I just bought a beautiful 240D at an auction. It looks like it was really well taken car of. Tonight when I tried to drive it the transmission would not shift. I pulled over and checked the fluid, it was low and I added to level. Then I checked for vacuum leaks and there seems to be none. But is still did not shift.

I did not drive it more than 15 miles and hour, so I don't know if it shifts at higher speeds. Anyone have any ideas as to possible cause or possible remedy?
Thanks