Has anyone modified a Miller & Kreisel subwoofer

Hello
I wanted to pose a question to the general audience here...I am the owner of a pair of ,,,well,,, not sure if you can call them vintage but Miller and Kreisel (M&K) S-2B's two way satelites with a matching V-2b sub.This is a great match for what I am trying to accomplish with my set up,but of late I have been curious about modifying the Subwoofer as I notice it is sort of slow and muddy,I would also like it to have more control,when I say I now notice b/c as my system evolves,these shortcomings are more evident.
I would also like it to have more control.
My question is this has anyone had any success with changing the caps within the sub,to maybe a teflon cap(faster,more transparent cap) ala V-caps is this posible?
I'd love to keep this SUB,is this an example of diminishing returns as the SUB is now dated?