Fuel leak sometimes?

[InternationalHarvester7.3]

My truck (1996 f250 7.3) Is leaking diesel from under the fuel bowl into the valley.. I have read through and seen people having the same problem but mine doesn't leak all the time? It only seems to do it every couple weeks and its not a bad leak its just enough to make me wanna fix it because diesel is so high.. My dads is doing the same thing and his also doesn't do it all the time? We have checked both trucks and we cant see any leaks or bad lines. My fuel bowl has been completely replaced about 50,000 miles ago so it shouldn't be doing this should it? Please help me if you know the problem.. Thanks!