Try holding the shifter up in park when you hit the key. If it starts then, or if it starts in neutral, chances are that the shifter linkage bushings are shot. There are two or three bushings and they cost less than $1 apeice. Remember that if the starter doesn't catch on the first try you have to turn the key all the way off before trying again.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.