last night there was alot of mist on my rear window so I switched on the rear defroster. After about 5 min, I noticed that only about 2 panels were defrosted and the rest of the windows stayed the same. Are the defrosters for these cars traditionaly that weak or is there something wrong with mine? I'm concerned that when the weather gets bad I will have a problem. Anyone have a similar experience? Can it be fixed?

My 84 318i has similar problem. My car had at one time gotten a fair amount of moisture into the interior; which corroded the "tabs" where the electric wires connect to the window defroster. CAREFULLY pull the leadwires/connector from the "tabs" and check BOTH for good connection....clean if necessary....be careful when you pull the connector off the tab---I literally pulled the tab off the window!!!--bummer.

The other potential problem that would cause what you are experiencing is a break in the defroster "trace" on the window. You can check this both visually and w/Ohmeter----to see if you have continunity of the defroster trace. There are repair kits (conductive epoxy) available at most good car parts stores----you can fix this yourself.
Bill in SF.