thielrules, I can't read your attached files nor do I have a 3.5 schematic.
Although the role of caps is to block low frequencies and the woofer circuit doesn't have caps in its series feed, there are some smaller values in the shunt circuits which could lessen woofer output via passing more bass to ground. But, my recollection (fairly dim) is that all those 3.5 shunts were mylar film caps, which have an indefinite life.
If an electrolytic cap has actually failed, it will usually show leaking goo. E caps are labeled "NP" for non-polar.
This gig is something that Rob Gillum may help you solve.
dsper, cap failure is a gradual thing until they might blow up, which should cause considerable sonic change. Gradual failing can be heard as frequency shifts in the xo regions, especially at high power and possibly noises like gurgling or sloshing water. As I mentioned, Rob has not seen any cap failures, Thiel used very high quality caps. The rule of thumb is 20 to 40 years of heavy use plus or minus 20. I'm not being facetious; if a cap is going to fail, it often fails in the short term. And if it's going to last, it generally lasts a long time. Yours didn't fail early, so they're probably good for a few decades.
Rob at Coherent Source Service could replace your E caps or talk you through doing it yourself. Also, we are developing crossover upgrades using 21st century passive parts. Our upgrades-in-development will not use electrolytic caps to address the fact that those interested enough to resurrect and upgrade classic Thiel speakers would be well served to never have to worry about caps again. The polypropylene replacements cost an order of magnitude more than stock NPs. We are exploring cost-effective solutions at two levels; it's a little early to announce brands, but we are making progress.
