Bob...I feel for ya!

I did this very repair this weekend...and like you chased alternatives
all over the place. My resolution was to take the wall access cover
off, remove and replace the upper assembly...finally life is good.

My problem started when I tried to drill the screws out, and of course
the brass is much softer than the screws, and the new holes drifted off
center, too much to recover. The correct drill for 1/4 NC tap is I
believe a number 7....yup bought them too!

BTW -- a local hardware store sold the upper assembly (brass) for $40,
where as the BORG sold the whole brass assembly including gaskets,
washers, nuts and all for $30. Replaced the upper half...now all the
lower half is left over. They also have plastic assemblies for about
half that.

Best of luck to you...

Darwin