The 5200A uses a RC oscillator (I think it was 10 MHz) to generate the clock. Mine was rather wonky. I replaced it with a DIP-14 TTL crystal oscillator.
There's one tuned LC - oscillator, to generate digital 10MHz for the PWM of the DAC, which generates a variable precision DC reference voltage of about 0.3 .. 3V, out of an SZA263. That's really great old school stuff.
The programmable / variable output frequency of 10 Hz .. 1MHz is generated by a quadrature RC oscillator, which has nothing to do with these 10MHz...
The output amplitude of this analogue oscillator is compared to that DCV reference and regulated to exactly the same RMS value by a fast precision rectifier. Also great stuff.
Although this design is pretty old, it's really precise and stable, if repaired properly.
Good luck, DefPom, that it's been the PSU subassembly P23 only.
That fat TO-3 component is a 5V regulator, 3A or 5A, not a transistor, and hopefully ok. (*)
The other transistors might still be available, or have compatible new parts.
Frank
(*) It's obviously an LM123K, a 5V, 3A regulator, still available, or replaceable.