If you haven't already, be sure and check the cowl and drain areas as well while you have the dash out. My 164 was stuffed full of 30 years of organic mess that had turned to rick black dirt packed solid from the rockers all the way up to the vents. Underneath the ECU on the passenger side kick panel is an access door that can be removed to clean out stuff. The vent panel on the drivers side comes out the same way. Take the wiper motor out to inspect around the hole. Stuff can become trapped around the motor shaft in the thin area of the cowl that it passes through creating a dam. The rockers have access plugs inside for cleaning as well. Removing the seat belt retract mechanisms from the inner rocker allows good access to get a vacuum cleaner hose in there .