<snip> The only advantage is the
heater, and that is marginal. <snip>

I now live in northern Maine and the heater in my '84 GL (1.9 wasserboxer) works so well it will drive the occupants out if the heat
lever is set to max and both front and rear blowers are set to fast .... even when it's -30 degrees F.

Could it be that those experiencing marginal performance have heater valves that are not opening all the way?

Mike