I ended up replacing the driver side window regulator motor with a working used unit. Now I have consistently working front windows (knock on wood). I suspect the rear windows probably need new motors and/or regulators as well.

Does anyone know what relay is needed for the rear intermittent wipers that plugs into the rear hatch (pic below)? Is it unique to this application or is it a common multi-purpose relay?

I located a w124 rear wiper relay 124-821-00-63, however it is an eight pronged plug and on my car it looks like a 6 prong plug