To check the fuel distributor for leak down you can run the fuel pump, then turn off the pump and remove the return line from the fuel distributor and watch for drops of fuel to leak out of the return port on the fuel distributor. After the initial dripping has stopped, time the number of seconds between drops. There should be minimum 5 seconds between drops. (this is a Mercedes Benz recommended test) Drip rate averages I have observed on the test stand are: 8 cyl. cast iron 5-7 seconds, 8 cyl. aluminum 8-12 seconds, 6 cyl. cast iron and aluminum 12-25 seconds, and 4 cyl. 15 + seconds.