Leaking air is the most common problem with these old instruments. You probably need to replace the rubber seal in the air chamber. An accordion repairer should be able to do this for you.
The 2 notes that aren’t working will probably be down to reeds needing adjusting/cleaning. Again, something an accordion technician should be able to easily handle. The reeds on the clavietta are very accessible, so you could have a look at the reeds yourself, and see if there’s anything obvious…
Sorry for such a long delay in my response. I need to replace the hard washers that are cracked and leaking. I found a few rubber washers that are not a tight fit that work but I would like something more solid or without so much play. I may have to make them if I can not find anything off the shelf. Any suggestions
I haven’t had to replace any of the rubber washers/discs, so unfortunately can’t offer any help here… It might be worth buying another non-working clavietta off ebay just for replacement discs? Do you need to replace a lot of them?