I recently acquired another learning project. I've been playing with it
in fits and starts, but I've been learning. The piston seal is shot. I
did a simple test blowing air into one side, and a little bit of air
could be felt coming out the other side.

I'm having some issue getting the plug out so I can try to pull the
piston out. It won't budge. The handy dandy 3 lb machinist hammer and
a punch won't make it spin. There was what looked like a wire dog and
slot of some kind on one side of the tube, but that was folded down flat
already.

I've left it set with penetrating oil soaking into the threads for a
couple days. I'll probably give it another go this afternoon if I have
the time, but I was wondering if there was something else I might be
missing. The plug didn't move at all previously. Using a pin wrench is
pretty much out of the question as previous owners and metal beaters
have already used the hammer and punch method on the holes and angled
them out nicely for the next guy with a hammer and a punch... alas, but
not for a pin wrench.