I've had a similar experience with a Hohner Ariette.
Some minor leakage is normal, but a big air leak is not good. If you have determined the joint is accessible, i.e. two frames butting together, replace the damaged or missing gasket with weatherstripping-type foam tape. That seal is rather small, probably 1/4" wide x 1/16" thick. Tub caulk would make the next disconnect difficult and messy.
If it leaks between the bellows end and the surrounding bellows end frame, your guess is as good as mine.
The typical hand-made Louisiana accordion has only two screws for the end plates, top & bottom.
These accordions should be tight, but not completely air-tight. If you close the bellows and hold up the bass side, the keyboard will gradually bleed down as outside air sneaks in. Tiny leakage will go unnoticed during play. However, if you can feel/hear the rush of air, it sounds like you have a substantial breach.
Thanks for information - I was kidding about the caulk.. haha!!
For now, I put some tape down the seam till I find something to replace the gasket with or see other suggestions to resolve this issue.
It is a very thin gasket. I could not hear a leak, but could feel it on my face when I put it up near the seal between the two sections. I noticed it since it seemed that couldn't get out as many notes with a squeeze of the bellows as some of the videos.
The tape helped and seems to work more like I expect it to. Not having anything to compare it with other than just a "feel" for it.
I should have started this music project when I was younger and was living in Beaumont, TX.
In NE Texas at my Daughters, just not many cajuns in this area of Texas. At least there are the online radio stations to listen to.