I used so once on a vehicle that hadn't been driven in a few years. Gaskets had dried out and were leaking. Think it's mostly alcohol that causes the gaskets to expand a little. Would try it if a valve cover gasket or pan gasket where there is no real pressure. Would have doubts about success on a head gasket. However, what have you to loose? If it doesn't work, you're no worse off than now.
2006 Gulfstream Friendship G7, Cat C7 and Allison 6 spd
Honda VTX and Crusier Lift on the back
Blue Ox Aladdin, Brake Buddy, 2014 Chevy Equinox toad