What is the plug?

[chuck nicodemus <armorseal@spiretech.com>]

On the back end of the head on a Ser ll, there is a square socket head
plug. What is it for and is it directly plugging the water area? Also if
so is it a "O"ring type or gasket type seal.? How deep is it into the
head and can you remove it without removing the head and or does' the
engine have to be dropped.??
I have a slight leak on start up but  it stops right after the engine
warms up. So far so good.

Paul, Jim Curt?
Thanks
Chuck