Incorrect, it pumps fluid in park just not at the rate it does in neutral or in gears.

Transgo has a replacement manual valve, it's included with their shift kits, that allows more fluid flow in park.

There are more things than the seal that can leak up front. Every bolt has a seal washer under it, a lot of times they do not get replaced. The square cut o ring around the outside of the the pump body can also be a leak point, especially if the surface it seals against is damaged or it gets damaged on install. Same goes for the bore the seal is installed in.