Since a cub is a flat head, there is no oil in the head or at the head gasket. If you have only recently purchased the cub, a good possibly is that someone put some water pump lubricant in the radiator not realizing the cub does not have a water pump.
"The Constitution is not an instrument for the government
to restrain the people, it is an instrument for the people to restrain the
government lest it come to dominate our lives and interests." Patrick Henry