Actually the 350 cylinder head was the updated one, I plan on replacing my original "14" head with one of those if it ever cracks. You are confusing two different problems DaimlerChrysler:
The 1986-87 300D/SDL/TD came with the 3.0, 603 that had the flawed "14" head. These heads will crack if overheated, but if you don't overheat them they will last for a very long time. I know of two with over 300K miles on them. MB revised them a few times: 14 are the originals then their was 15,16,17, and 22 is the new one. I think their might have been an 18 or 20 in their. But any head over 17 is fine.
Now the 1990-1991 350SD/SDL had a weak connecting rods, the rods of the originals will bend causing the cylinders to oval out and ruin the bottom end. Their is a 50-50 chance to a 60-40 chance of one going bad, depending on who you ask. Buy one with lots of miles. Figure $6k give or take to replace the short block with an updated one.
The W140, 300SD's used the same above mentioned engine from 1992-1995 in the US. The 1995's are supposed to have the fixed engine's. The 1995 300SD is a nice car if you can find one!
