a gut reaction would be that if the engine wasn't occasionally turned over during the off season, maybe the seal slightly stuck to the crank, causing it to tear ever so slightly or deform a tiny bit, causing the leak ?
as to using the right stuff, i wouldn't use that myself.
as i think Cab [?] said, a clear silicone "adhesive" is the stuff to use.
"adhesive" needs to be on the label.
https://rainbowtech.net/wp-content/uploads/88000-Clear-RTV-Silicone.jpgi like this stuff, but i'm sure there are other products out there that are like this.
