I didn't think about the electrolytic power supply caps, that is a good point to bring that idea up! They are certainly old enough.
The Teflon caps replace the film caps in the unit, so this is just a sound quality improvement. I am not sure what film caps are in there, most likely polypropylene, but that is just a guess.
I'll open up the units tomorrow and take a look at what is involved with replacing those big PS caps. Unfortunately, to work on this unit requires removing about 20 soldered in place wires - they didn't use any connectors to connect the motherboard to the chassis wiring.