I have a 99 F350 SD with the 7.3l that had a similar problem. On the fuel
filter bowl there is a bleed off valve that you can use. This is so when you
change the filter, you can drain it a little so it doesn't overflow. On this
bleed off valve there are 2 small o-rings that the fuel goes through, these
will get hard and will start to leak. It cost me like $0.05 for the 2
o-rings at my local auto shop and 20 minutes worth of my time. Make sure you
wear rubber gloves unless you like to smell like diesel fuel.
Give this a try.

Buddah

I have a 97 f350 7.3 turbo diesal and had a fuel leak and mine was coming out
of the lifter pump right behind the fuel filter housing