Re: the SRR-13.
I had one long ago- 50 years.  The band switch
 is mechanically wonky, using right-angle levers
which are clamped with a screw to a shaft
in the removable band modules. 
The levers are pot metal and
very brittle- they crack and break at the clamp.
Never found anything that would sub for them.
Glue was useless.  I don't know
what kind of metal this was but epoxy
didn't stick.
I liked the set but gave it away after
beating my head on this problem.

Have any of you solved this?

73 OM DE Dave AB5S