Yes, that non-hermetic C3 is a wet-slug Ta cap. These are quite special
(and expensive), and can be amazingly good, or cause lots of grief if
they leak. The key is in the seal around the Ta positive lead, and how
well it holds up over time. Ultimately, the cap either loses its
necessary
As Corby said, check for the 137 Hz signal first. If that's OK, I think
the simplest thing you can do before taking things apart, is to look at
the adjustment pot for the 274 Hz amplitude. Mark its position, then
tweak it end to end a number (like tens) of times, then back to its
original
