That's a nice find, Max. I would replace the lytic and go from there. However, also replace that oil filled cap too before going any further. You should replace that one with another oil type which can still be found in the same physical size. Be extremely careful when handling the old leaky cap. Those oil filled caps before 1979 contained PCB's which you don't want to touch as that stuff is bad news to your health. Absorption through skin contact is what you want to avoid, so be sure to wear gloves when handling and cleaning up any residual that may have leaked in the cabinet.
The oval oil caps can be found at McMaster Carr.
I believe MMC part number 7602K23 will work (it's rated at 3.8-4.2 uF), but verify the can dimensions as it should clip onto the chassis just like the original with a retaining clip I believe. The original 3.5 uF is hard to find new now, so the 3.8/4.2 would be your best bet.
https://www.mcmaster.com/capacitors
Grainger also has the oval caps. The Dayton 4 uF would also work:
https://www.grainger.com/search?sear...oval+capacitor
The electronics supply houses like Mouser don't appear to carry a wide range of these caps, so the industrial suppliers seem to be the best answer.
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