Sorry to hear of your troubles with the sightglass. Another
common problem.
My 90 leaks at the boiler/sightglass joint but still works
as the engine doesn't need much pressure. The previous owner
glued it in with a silicone sealant, and while the fitting
is still loose it works. I'll fix it when/if the leak and
'Pressure Drop' (Toots and the Maytals) gets to be too bad.
Good Luck,
Wayne