I just got an old 20s-30s banjolin. No brand on it anywhere, a luthier at a local folk music center told me it's probably a Maybell. It's in pretty rough shape, a good amount of cracks, but it's repairable. The one thing that i'm most concerned about is that there is a crack on the fretboard. It's a pretty good size considering how small the neck is, probably about 3-4" long. I took it to a guitar tech and he told me not to glue it because it might damage it further (something about the frets getting messed up). He suggested oiling it and leaving it alone.
Does anyone have any advice on how to fix this? Also, what is the best glue to use? most of the cracks are too small to pull apart and apply glue on each side. I'm thinking I need something with less viscosity so I can apply it on the surface of the crack and let it seep in.