Ha! Mr. Schwartz indeed.
The lock mechanism does not remove easily, so don't bother trying that. But you can check the lock plunger very easily – if you push it down a tiny bit and the buzz stops, that's the source! Here's what to do:
Be cautious with the rags used to clean up linseed oil. As it hardens it also gets hot, so if soaked paper towels are balled up and thrown away they can catch fire! It is recommended that you spread rags out to dry someplace safe, then thrown them out after the oil has dried.
Good luck with this The list of potential buzzes in pianos can go on forever, so the other advice I have with a really difficult to find buzz is to have a friend help. 2 piano tuners are definitely better than one in these cases.
The "Amazing Mr. Schwarts" San is correct.Have implemented this "fix" often also appropriate on the S&S Boston pianos.My glue of preference for this is either Elmers school glue ( dries clear) or the titebond molding glue.Both have similar results.