sweet you have a Crabb, i have one too. it's good for anyone giving advice to know the age of the instrument. time has effect on natural materials. good advice you've gotten so far, but to analyze without having the instrument in hand is really just a guess. if i were new to concertina and repair, i would have someone of good reputation take a look and set it up right. That might cost you a fair amount, but if it's a newer Crabb, maybe not so much. There is a huge database here if you want to try it yourself, and yes, get the David Elliot book first.
w.