Nice video, helps me to watch someone do it before I do mine. Your PTO clutch isn’t supposed to spin like that. See the stud sticking off the frame, it’s supposed to notch onto the little key hole on the PTO flange. It just keeps the pto from spinning. That’s probably why your plug got ripped off when it spun around.
The oil leak is likely the main crank seal on that Briggs unit. They all leak there it seems.

Great video. You did a good job explaining how to fix. You probably saved 200.00  by doing it yourself. Thanks

Thanks for this upload.   I've noticed on my mz6128 that the motor mounting bolts tend to vibrate loose over time so I have to re-torque them every couple years plus added lock tite.   Also,  these engines vibrate pretty good and if the oil filter is not tightened sufficiently they also work loose and bleed oil.  Those hydro cooling fans could use a good blowing out with a air wand.