Speaker Re-cap. How do you know when?

Howdy. Looking for input on speaker capacitors & their life span. I have a set of Infinity Renaissance 90's and the bass seems to be thinner than it used to. Thinner meaning not as strong, feel it in your chest type bass. The speakers go down to 27hz, so I know form the specs and experience that it can happen. Reason I am asking about the capacitor, is "back in the 70's", I had a pair of Pioneer speakers that occasionally would literally blow the insides out of a cap. I'd go to Speaker City grab a new one & solder it in till she blew again.
Question; Is there a chance the caps are old & hammered or am I searching the wrong area? What have you folks experienced? Are there even caps in the woofer cross-over’s?
Speakers are powered by Krell KCT pre & Krell FPB300cx.
PS - The surrounds look like new.
Thanks for any input and advice.
You may want to open the speakers and find the largest capacitors in the crossovers, then verify if those caps are in paralell with the woofer(s).
Assuming that Infinity used a second or higher-order crossover, you will find an inductor in series with the woofer(s), then a cap in paralell. If that cap is leaky, some of the symptoms could be weak bass or too much midrange, which sounds like weak bass.
To avoid frequent replacements, buy caps rated for at least 100 volts. Nonpolar caps are better for crossover duty than regular, polar caps.
Good luck
Getting better caps can also improve the sound. Silver wire or higher quality copper can also be a big improvement.
Make sure there are no air leaks. Make sure all drivers, binding post, etc...are all secure.

Electrolytic caps usually last about 20 years, so it's probably time for a recap soon anyway. If possible, use all film caps. I believe those speakers are somewhat forward already, so I would avoid Solen caps.
I found a cross over scematic last night on the net. I'll do some research on the matter. I like the note about air leaks. While all looks A-OK, I'll double check. I am not that much of an elctrician to know how to check the cross overs with an ohm meter, which is how I suppose it should be done. I see Humble Homemade HIfi has done some capacitor comparison which looks cool. Anyone know of a good reputable shop I could send the cross overs to to have them checked & possibley tuned up? Probably would'nt hurt.
Thanks again, John
If the bypass cap on the woofer is blown then the woofer is more like a Full Range driver then a low frequency driver.
If you want to send me a copy of the schematic I can help you with the parts. My hobby is updating crossovers and having the schematic is half the battle! I have updated a pair of JBL L300s, a pair of Altec 19s and two pairs of Dahlquist DQ-10s. I am currently updating a pair of JBL 250Ti’s.
Sonic Craft Sonicaps give you a great sound for the cost, Solen inductors are also great for the price and Mills resistors are very good. If you want to build the best Duelund components are the way to go; their resistors are the best bang for the buck that I have found for resistors in the signal path.
The Ren 90'S use the Watkins dual voice coil woofers and there are NPE's in series with the windings. It's very possible that the caps have either lost capacitance or become very lossy which would result in less bass. I'm pretty sure the 2 ohm winding is driven by a 100V 880uF NP electrolytic but you will need to carefully remove the woofers to double check the values. If you do replace them then make sure to select the highest quality caps you can afford because it will affect the bass response and distortion specs.