I recently replaced all four coupling caps in my SLI-80 F1 after one of the original Jensens failed.
There are lots of options out there but my recommendation would be to contact John at The Audio Connection in Seattle. He's a Cary dealer and very knowledgeable about upgrade and repair work on Cary gear.
He replaced all the caps in the amp including replacing the coupling caps with Cardas Golden Ratio capacitors. They're no longer produced but he has a substantial stock of them. His repair work is very reasonably priced, making it cost-effective to pay the shipping to get the amp to him.
And, yes, the Cardas caps did sound better than the Jensens, which were themselves an upgrade from the stock SLI-80 caps.
Yes, If you are going to ship or hire a tech, might as well replace all four IMO. I had those Jensen oils in my former SLI-80, they do produce a softer and more veiled over sound in that amp. If you like it, can always stick with it.
While I have the same caps in my Cary preamp now, doing some testing with a few friends who opted to go with the upgraded Mundorf's that Cary offers as an option. Any good tech can source the same caps as suggested above.I ran the Mundorfs in my prior Cary amps and current amps from another mfg. More open, clear, with nice texture. It varies.
As others have said, each brand/type/model cap can all produce a different sound and result. Its worth figuring out what you'd like to change about the sound if you are going to replace all four caps.
@analogphotog if replacing, its best to verify what uF and voltage caps you have installed now, and if it's helpful to know if they are stock caps or not. If its a used SLI-80, people change them. People sometimes go 1000v when less is not available. May not be necessary, check the caps you have inside now, first.
Having owned the Cary SLI-80 Signature and the Cary SLP-98L tube preamplifiers, and comparing with friends, I've concluded one thing. Changing caps may not always be an improvement, it can offer a "different" sound. It helps to know what you are trying to change to gain more or less of in the sound, if that makes sense.