Ok so there are 2 cars i have in mind, one is a 1980 240D with a 4 speed manual for 800 dollars, but I'm sure I could talk the guy down, the problem with this one is that it has a rod knock. The other is a 1983 300DT automatic for 500 dollars, the problem with this one that it smokes like crazy. I think that means a ring job? But im no totaly sure. They are bolth in good condition other than that, but this is my first car, and my first mercades so what should I do?