Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

I say 'Dimples in'
JB sealant - just a bit inside the inner area between the
glass tube and seal sheet (like smoothing a glue joint) ought to do it.
You have to assemble it first, apply the sealant as described above
and then mount it.  I've also added a tiny bit to the screws.  Just a
smidge, it will help seal and might also act a bit as a lubricant when
screwing it in.  If it looks good...

Works for me.  Then again, each time I do a sightglass is an adventure,
and not always with a good outcome.  So, you try again.

Good Luck,
Wayne