Should I buy used Thiel CS5

The CS5 is certainly one of the better Thiels ever, especially regarding bass reproduction (sealed woofer) but, as others have noted, needs a lot of current to drive properly (and quality current is $$$). $3K seems pricey to me for a speaker that age. You will want to replace electrolytic caps.

If you like the Thiel house sound perhaps but you need to familiarize yourself with this sound before buying. One look at the crossover on this speaker could scare the hell out of any prospective buyer. The tweeter on these older Thiels some find very objectionable.

You will want to replace electrolytic caps.

No electrolytic caps, all plastics, last forever (well almost)

https://www.whatsbestforum.com/data/attachments/17/17403-3e3aa52a4bb8c32c4dab3b281e022f17.jpg

" The CS5 crossover is itself also heroic. Constructed on a single hard-wired board, it incorporates 87 elements realized with 114 components. Only—only—55 elements are directly related to the first-order high- and low-pass filter functions, the rest being used to fine-tune the system’s time response. The two midrange units, for example, are electrically "moved backward," by the equivalents of ¾" and 3/8" respectively, to bring their acoustic centers into the correct alignment.
All coils apart from one are air-cored, and the capacitors are polypropylene and pure polystyrene types, the latter custom-made with tinfoil plates and copper lead-out wires. The internal wiring is a polypropylene-insulated solid-core type."

The tweeter on these older Thiels some find very objectionable.

I only found that with with bad recordings or soso electronics, same also goes for the CS7

No electrolytic caps, all plastics, last forever (well almost)

Holy cow! That's a crazy number of parts!
It does *look* like there are 2 ELs at the bottom of the pic, maybe a couple more at the other end? But, yeah, mostly film caps (PPTs and MKPs). Nice.

Still, *I* would upgrade the resistors and probably some of the caps for better sonics if not to replace drifting ELs.

I dont care what quality of parts you put in this crossover it is an abomination in terms of complexity and total number of parts. Seems to be a very complex way to approach whatever problem Mr Thiel was attempting to solve. When I look at a crossover like this I simply scratch my head and wonder why.