manuel pump

After some looking around and tightening of fittings I've discovered that what makes our 82 240D run well when it's cold is to operate the little manuel pump until a clicking noise comes from the main pump body.
Then the motor cranks and runs well.
When the motor is warm but not hot, I sometimes have to do this to get it to start at all.
Does this indicate anything to anyone? There are no visible fuel leaks anywhere near the pump or filters. I've bled both filters.

Thanks for any ideas - Harvey Surlive