I followed Euro 287's advice and had all the vacum lines checked. The lines that control all the valves/air flaps with vacum switches and the "vacum pot" behind the instrument panel. The diagnostic was not expensive: 1 hour of labor. The good news was that all my vacum lines were fine and that, there were no leaks. The bad news, however, was that the mechanic concluded that, because the vacum switches were working, the blower motor had just been replace and the air flow was still so reduced that, the vent flap comming out of the heater core must be either stuck or broken or jammed (somehow permanently fixed at 1/3 open). Fixing this inexpensive valve would be very expensive. It involves, my mechanic explained, about 13 to 14 hours of labor to remove the dashboard and locate the valve at the base of the heater core and replace it. It's so expensive to fix that I decided to live with the reduced air flow problem and keep my air on "low."
Then, as luck would have it, I decided to take the Benz dealer up on his offer to let me trade in my old 87 300E for $9K against a 1999 C43 AMG (w/ 40,000 miles)(Black on Black) just brought in off lease. I'm very excited, and should get the newer car this Friday.