Yes you will have to get the dishwasher out to replace the bits. Get the machine out and remove the side to view and work on the problem. The parts are a strip of spring steel, a spring and a fixed plastic guide that you thought was a wheel. It is usually the plastic guide that has broken and caused the spring tension to be lost but have a good look at all parts. You can remove the parts on one side and still use the dishwaher but you will have to keep hold of the door when opening it. The door spring tension acts as a brake to control the downward motion of the door. Find out what you want and order the bits on line. If one side has gone the other side will also be near to failure so do the job once and for all. It is a bit of a fiddle with the spring but mark which hole the spring is in from the good side to get the door tension right.
peter
November 2008