450 diesel pump

my 450 has the b type pump with the IH on it ive put the new seal in the lift pump but i am still getting fuel in the pump what else my be leaking? thanks

Well, presuming the seal is actually working and you got both the thin and thick gaskets back in place with no isues, then it would be back flowing in from the tank return line. That isn't real likely, due to the long standoff pipe inside the tank on the return fitting as well as the pressure relief needle valve being in the way inside the pump. But if the stand pipe is broken/corroded and the needle seeps well then maybe...
There may be something I'm forgetting, but I consider those to be the most likely. Otherwise the plunger assembly has a leak, and that would also require some needle valves to leak as well.

The most likely place on the B pump to leak fuel into the pump oil sump is the orings on the delivery valve tappets. Requires pump removal & complete dissasembly to replace them.

That stuff is supposed to end up drained overboard out the vent. Unless the vent is plugged... Hmmm.

the over flow drip pipe dose have fuel dripping out some times and no fuel comes out of the return from the tank with the line off. is it possible that the return line from the pump is pluged? thanks

Well, if it is, you can find out by blowing through it.

Heres the questions to ask. Does it fill just sitting? Does it fill when running? Or both?

The A and B pumps handle fuel somewhat differently although they are nearly identical. Both have a pair of needle valves to regulate pressure, one inside the primary pump, and another at the inlet to the plunger assembly. On the A, pressures are set to 60 and 75, meaning that the primary pump handles regulation by venting at 60 psi back to it's own input. On the B, pressures are set to 75 and 60, meaning that the plunger inlet handles regulation. With no scavenger pump to pick up the excess, it vents out the back into what becomes the tank return. That is why the return line is up there on top coming out the back side of the plunger assembly.

Both pumps assume that leakage from the plunger and distributor valves will dribble into the bottom somewhere. The A routes this to the backside of the primary pump (it is a dual pump) via the scavenger valve and sends it back to the tank. The B assumed that the pump internals didn't leak enough to matter and just dump it overboard. Obviously when worn, things change.