Don --

I've repaired the heated seat (driver's side) in my '86 245. I am quite sure the bulb and heating element are independent -- that is, whether or not one works has no effect on the other.

There are two elements -- one in the seat, and one in the back. They are connected in series, so these are dependent on each other. If one fails, the other will not work.

The lower element has a small thermostat in the grid. This thermostat is about the diameter of a nickel and perhaps 3/16" thick. A common failure is the connection to this thermostat. After being sat on hundreds or thousands of times, the connection finally breaks. It can be resoldered (as I did), but a good idea is to attach a 1-2" pigtail between the heating wire and thermostat connection to relieve the mechanical stress and prevent another early break (as I did on the second repair.

If you decide to try this yourself and are comfortable with minor electrical work, I'll describe the disassembly process. A few mechanical and electrical tools and needed.