EBarnacle says ....

"Subject: RE: Cost to repair/refurbish a concertina
From: EBarnacle - PM
Date: 22 Aug 18 - 01:28 AM

Gargoyle is right. The sticking buttons are very likely due to dried felt rings around the buttons. Use the very lightest oil you can find. Do not use automotive oil or 3 in one, which is 30 weight. Sewing machine oil is good. Go very light on the amount you use."

Dave Elliot's Concertina Maintenance Manual says .....
Page 4. Basic Care. ..
..
No. 8. Do not lubricate anything. It will collect dust and gum up the works
..

Jake