As far as your heater is concerned, you may have a bad thermostat. Pay attention to your temperature gauge, and if it is not reaching its normal operating temperature than the thermostat may be stuck open. This happened on my 300SD and the car produced very little heat.
1976 300D (W115) - 330K and still going (sort of)
1991 300D 2.5 Turbo - Sold at 221K
1983 280SEL - Sold at 206K
1981 300SD - Sold at 232K