"Stop leak" at Canadian Tire (yellow tube), it works for my neighbor for 3
years.
And for me for 1 years (probably more but I had all winter to change the
gaskets)
Specially for the head gasket, not good for major leak but this small
particle powder can do some amazing job. Many will say that it clogged
radiator (and heater radiator), I don't believe that for a minute. I change
all my radiators last year and open the front one to look inside just for
fun, no trace of nothing. After changing my heads gasket, both surfaces of
my head where clean and without any "dent"

So it's not peppercorn but is a non-expensive short-term solution.
Ben, Montreal