JFLEISC wrote:
I had what I thought was the same problem with my 0-300D.

FYI - If by chance the leak is between the upper end of the pushrod
tube and the cyl head, there is only a metal-to-metal seal between the
two. For field repair, a multi-ball type expander tool is used to
expand a bead from the ID of the tube to get it to reseal. Sometimes
the tubes get loose during misc jug handling. It is a simple fix when
you find someone with the tool.

But you are smart to be absolutely certain where the leak is first.