Me again,
Sounds like were in the same phase of a restoration. I cleaned my oil tank yesterday and noticed the sight glass was loose. After I flushed and cleaned the inside of the tank I cleaned up the area where the sight glass sits and put a small bead of 3M yellow ultra high strength weather stripping/gasket sealer around the recessed area where the sight glass goes. Then slid the glass in. I've used this 3M stuff a bunch on my 1970 land rover, mostly trim type applications but it holds very well. It does say "gasket sealer" on the tube so I figured it will be ok with oil and the tank is not under pressure so it seems like a pretty safe bet. I'll keep you posted. I have a feeling any silicone type sealer would work, may be someone will chime in with something that has been tested. Worst case if you try something that fails you will see the leak and its easy to get to if you have to make a repair.
pb
