General question, I have a ss Hardin gen6 pump that is pushing oil out of the front seal. Totally rebuild pump, 2 new front seals, still leaks out the drive fluid. Any ideas? Hardin says possible fuel pump causing too much pressure in the reservoir, I don't see any fuel in the yellow line.

Have you checked the lube level to see if its fuel contaminated and overfull?? Every fuel pump/sea pump I've ever seen gets some fuel in the lube over time.
The yellow hose usually won't get fuel in it unless there is a major failure of the fuel pump diaphragm.

Not familiar with rebuild the hardin pump, just the Merc
If the hardin uses different seals the Merc as it does with the impeller Gen 3 housing, this might be the issue. Suggest checking the parts listing

Surprised Hardin told you that. I have the same pump and they have an accomodation to vent the reservoir. There should be an 1/8 in. plug.

Look at my picture. You will notice where I vent the reservoir into the fuel pump vent line.

Sorry for not updating or posting. Was gone on a M/C trip that got cut short due to approaching weather. Fuel pump was off the first time and no leaking of fuel into oil. Hardin says Merc parts are interchangeable. I did not know if my pump had the vent line drilled, it does, that may be a solution. May have some time today to pressure test fuel pump and sea pump. Got new front seal /inner seals in mail while I was gone. Will update when I get something to report. Thanks all for your suggestions.

I actually had to change both of my raw water pumps essentially due to fuel in the reservoir, poor maintenance by the last owner. I am considering elec fuel pumps to replace the manual pumps. I will plumb it so in the event of a failure I can switch over and have one pump feed both motors to get back to the ramp.

Tested fuel pump yesterday. Put 10lbs of air pressure on the inlet and held my thumb over the outlet. Put a vacuum/pressure gauge on the pump vent outlet, pressure reading was about 10lbs. That indicate a leaking pump which might be the issue. Also took fill plug out of sea pump and pressurized it. No leaks that I could see. More updates to follow.

You hear a lot of fuel pump failures diluting the oil reservoir. My next move is a block off plate and electric pump on both engines.

Installed a makeshift vent onto the sea pump. Ran boat on lift, oil up tube a inch or so. Took out for a run up to 5000 Rs, pumped oil about 6 inches up, then settled back down at idle. Went out and picked up a new fuel pump. Not cheap, Mercruiser part prices suck. Topped off drive fluid in pump, took out for another run. Had a leak in my makeshift vent, had to run to hardware store for a new ferrel. Will patch that up today and give it another try, but the leak is telling me the cavity is still getting pressure from either the fuel pump or some other internal issue. Sent a email tech request to Hardin yesterday explaining the whole deal. I will see what their response is. Looked at some knock off merc pumps on line last night. That may be the answer down the road.

There is only 2 places pressure can build in the pump reservoir, fuel pump or bad seal on the impeller side forcing water into the reservoir. That should be obvious based on the color of the oil.