If it is the seal, you must remove the Roto-Stop (blade clutch) and blades, then pull the engine off the mower deck. When inverted, you can inspect the bottom, oil pan and seal area. I do not think you have to pull the pan off to replace the seal. The shop manual shows a special tool is needed to drive/seat the seal properly.
If you are going to attempt this level of repair, I'd urge you to get a factory shop manual and save yourself a LOT of grief:
Honda Power Equipment Shop Manuals on eBay
Honda Power Equipment Shop Manuals on Amazon