Hi Oskar, I have two old Lachenal anglos 20key and 28key which Dave Elliot restored for me a few years ago (Hi Dave!).
I can attest to Dave's skills in fixing concertinas and as suggested earlier you should buy his book!
My 20 key anglo was shown in Concertina.net years ago when Paul Schwarz was running it.
Dave - sorry but not been playing. Our choir is doing Bold Riley this term so might get to perform, after a LOT of practising!!
Oskar, good luck and hope you get the old Lachenal working again. Cheers, Phil.