I have a '79 300D which is becoming increasingly harder to start in the mornings. I do not live in a cold area, infact it was in the high 50's/lo 60's today and it took a good 1 to 1 1/2 minutes of glowing before the light went out. Then I have to crank it for 10-15 seconds to get it to "catch". I have been told the glow plugs are fine as is the electrical, battery, etc. I've never had a Diesel, is this normal?