I bought my 1983 300sd new, it came with 4 years or 48,000 miles warranty. I used it as a daily driver. A few years ago, when I could find Synthic oil at walmart for about two times the price of normal oil and my 300sd had over 100,000 miles on it, I swiched.
My 300sd is still my daily driver and has 230,000 miles on it. It get 26 to 30 mpg and has pick-up and go.
I change the oil and filter myself every 3,000 mile and it does not need any oil in that time.

When I have to use a rental or my wifes Volvo, I love the 300sd more!

I may not need to change the oil every 3,000 mile but I look forward to it.