Scotty Kilmer is actually pretty knowledgeable compared to a lot of guys on the youtube. I've watched a lot of his stuff and haven't seen any bullshittery yet.
Normally, like he says, a lot of this type of stuff is snake oil, but there are some products that will swell/soften seals enough to stop a leak.
Now, realize that seals and gaskets are different, like he says, seals seal around shafts that spin or slide. So, there is all the possibility that this stuff will work if its in the correct situation it was designed for. The type of stuff that may do more harm than good are the products that have particles in it that plug up the leak. Those may clog up small oil passages and cause oil starvation. This stuff is just a liquid so it seems safe to try.
I've had pretty good luck with the stuff. On my old Tracker (with AT) a small leak will develop around the solenoid and prevent the torque converter from going into lockup. One bottle of the stuff and that little leak sealed. It was nice to have lockup again since it didn't have an overdrive.
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