1983 300SD. Still have a hard time finding out what is wrong. Car need to be primed with the hand pump before it will start in the morning. After that it is good to go all day as long as there isn't a few hours between starts.

I left the fuel cap ff for the last two days to see if the vent was not working but it did not change anything. The fuel filters are fairly new but I will change them out today again.

It seems like air is getting in somewhere. Any other suggestions?