John,
Those are good capacitors, they shouldn't be wearing out, in my opinion, they are silver metalized polypropylene capacitors if I am thinking of the correct capacitors. What kind of tubular does it take? Do you have a schematic, or is there one online? What kind of power supply does it have, a CLC, or a CRC type?
Personally, my favorite capacitors are Solen Capacitors, although these low ESR electrolytic are very nice as well, especially where you don't have the room for Solen.ca, just not as smooth. The only film caps I have personally tried in power supplies were motor run caps and they sounded nice, but then again not as smooth as Solens. Part of what makes some caps sound better in audio applications is caps built so as to resist vibrations and ringing. Other factors are electrical, but these physical factors play into this all as well.
If you want to change out those capacitors you could, but I would rule out some other factors before I did that. I thought film caps were supposed to last several decades. That large blue no name cap would be the one I would start with, I would replace it with a good quality audio electrolytic.
Something like these I would try: http://solen.ca/product-category/capacitors/ at same time you will get warranty from the Solen manufacture