Any significant DC leakage in a crossover capacitor generally means there will also be some degree of low frequency AC(signal) or parts thereof passing below the intended knee point. Pretty much what you don't want in a crossover filter, and why it's important to test them for leakage as well as ESR when possible or replace them after a reasonable life expectancy has passed.
We are after all talking about caps that are 60 or more years old, and hardly came off the top shelf when they were new.