life span/failure rate of filter capacitors?

If it were my amp I'd do it, minimally it will allay your doubts in regard to their possible failure, and if you're keeping amp for the long term they'll have to be replaced at some point.

Thanks, @sns  , I would like this amp to last longer than I do, if that is possible.

I just got done looking on partsconnexion, & this may not be as easy as I was thinking it would be (finding one with the specs I want).  I'll do a search on the others you mentioned--Mouser, Allied.

If worst comes to worst, I guess I can email Cary & try to buy four of them there.  Back in the 90's I bought a "power-bank kit" (added filter caps and an umbilical cord to attach them with) for another Cary amp I had, and I am going to look, but I am thinking that they were the same value.  Cary's prices for signal caps are crazy, though, and I suspect they would be for filter caps also. 

Regardless, thanks, & I'll look at those other places you listed.

Depends on a lot of variables, size of the capacitor (larger caps don't get hot as quickly as small caps) if it's placed near hot areas of the amp and quality of the capacitor. Most of the really large caps of high quality usually last a lot longer than all the smaller caps in an amp.

Eric has provided good advice.  Plus you may also begin to hear fluctuations in the music with power capacitors.  If you are in the NYC area I can take a look at your unit.  On Parts Connexion look for Nichicon Super Through parts.  You can go up in value if you have to just make sure that they fit in the space you unit has.

Much has to do is how much demand on them in the circuit ,better to have more smaller caps lower distortion ,  how hot is the area and how much use .

failure much higher in amplifiers ,quality too of the caps has a lot to do with it . 
caps get dried out as they age .