2021-09-27 What's Behind These Leaky Plugs?

No surprises behind them Don. Just oil gallery machining access points. the ones that look like a shouldered nut should have o-rings under them. There are a couple of plugs on the back side of the oil pan that are pipe plugs. The 2 in your pic look like they have silicone sealer on them? Maybe the previous owner opted to leave off the o-rings and just used silicone sealer?
The only caution I see here is the integrity of the casting that the threads were machined in to. I've seen similar plugs and when someone tried to break free with a Johnson bar and socket the shouldered nut plug, the casting cracked. It's a good job for an impact with a light touch to break them free, then deal with the leaking issue. 
According to the torque chart on pg 37 of the manual, the "oil pan passage plugs at oil pan"are a 20mm x 1.5mm to be torqued to 16.5 lbs/ft