I repaired our Ab/Eb Jeffries concertina last weekend.
1 Settin the Reed
The low F reed on the left-hand side sometimes had stalled on initial button press. So, I increased the gab between the reed tongue tip and the reed frame slightly. Now, it never stalls!
This is the reed pan of the left-hand side. Reeds of low notes are much more difficult for me to set than ones of the high notes.
2 Patching the Gusset Leak
Our Ab/Eb Jeffries has old bellows. I patched a gusset leak using a piece of leather.
First, I patched it from inside the bellows.
Then, I patched it from outside to make sure...
It took a few hours to repair it. Now, it's easier for me to play than before.