Front seal

It is not very hard. But check it over close, these engines like to leak between the front cover as well.

Remove the serpentine belt. Jack the vehicle up on the front right and secure it with jack stands. Remove the converter cover and stick a bar in so the engine can't rotate. Remove the balance retainer bolt, it was installed at 92 ft. Lbs. Next hook a three jaw puller to the inner hub and pull the balancer.

Check the balancer real close, if the rubber shows any signs of age like cracks or if it has a lot of oil on it, replace it. Check the hub area where the seal rides for a groove worn into it, if there is a groove you might be able to use a speedi-sleeve on it, but I would probably replace it because of age and oil.

Remove the old seal, use a seal installer to install the new seal with a thin coat of Permatex on the outside. Use a balancer installation tool to install the balancer, apply a dab of sealer in the key-way area before you install it. Tighten the bolt down to 92 ft. Lbs.
Probably replace the belt if it got oiled as well.

All of the tools should be available as rental/loaner tools from a parts store, if you have places that do that.

Keep us in the loop please.

The 3.9 is known for bad crank seals, valve cover gaskets, oil filter adapter and oil pump drive oil leaks. Somewhat easier way to fin the leak is to get a bottle of UV dye from the parts store. Or online. Then get a UV light, these are handy for more than just oil leaks. One good one I've found that is much less expensive than most is a Rayovac 9 LED UV Flashlight it was 10 bucks at walmart! Wash/wipe the old oil off. Add the dye to the oil. Start it up and see what the UV shows. Just don't try looking out in bright sunlight.

This is what the light looks like.