Update, the seat is still soft, no splits no rot and looks good too. I applied a little more this week and wiped it down.
I tried it on the 1969 tool bag, it was so hard I was afraid it would crack, after an application and a soak in the sun it's as soft and flexible as new. I put some on a newer thinner tool bag, it got so soft I thought I had ruined it but after a day or two it's looking good again.