I agree with John Grant, regarding the factory-installed construction
plugs on the sides of the intensity valves (2,4,6, 7), each block held
in place with four screws.  One factor that is sometimes overlooked is
this:  After years of expanding and contracting from various levels of
humidity, slight shrinkage of these plugs small leaks can occur around
the edges of the plugs.  Test these areas for leaks and seal them if
found.  They can be sealed with glue, or a small piece of rubber cloth
glued over the area.

Bruce Clark