A brother-in-law of mine has owned the CT 100 from the same series for a long time and is very satisfied. I like them with him too and you wonder why you spend money on high-end stuff at all. (They are good, but I made a different choice). In his box (bought second-hand), the tweeters were exchanged for others and caused problems after a while. A phone call to Canton solved the problem and he received two new tweeters (for a fee, of course). This also reflects my experience with Canton, e.g. the Karat M90 DC currently in my possession, where the dust cover of a woofer was damaged by a cat. A statement about this was woofer costs 140 € roundabout, but an exchange would be necessary for optical reasons. The company keeps spare parts for a long time. At least here in Germany it is not a problem.
If there is no - visible or audible - error, I would open the box out of curiosity. But due to its age, there is a risk that the screws in the housing material will no longer grip securely afterwards. It used to be recommended to carefully retighten the screws after a while as they loosen over time.
If the box is open, you can of course take a look at the crossover and the damping used. If you then want to improve something, in my experience suitable measuring equipment is urgently recommended (at least REW, Arta, and the recommendations for microphones and interfaces mentioned there ... Boxsim, VituixCad and MCmachina can also be helpful). Then the path of do-it-yourself and try and error and many attempts begins. Nobody will do that 'just now'.
Of course you can exchange all kinds of things because things are old and 'high end recommendations', which you are guaranteed to hear but cannot measure, will be found in the many other forums that deal with it. Fortunately, it is fun when you start and you also have the feeling that you have done something good and everything will get better, you always only know afterwards if that is the case.
Even the replacement of all electrolytic capacitors - which is due to the aging process, which is stronger with these components than with other capacitors - I would initially strongly question. In my opinion, this does not involve a suitable component tester, which in turn means measurements. Boxing is certainly there to be heard, but with my experience today, I would not trust myself to make changes by ear.
https://www.hifi-wiki.de/index.php/Canton_CT_120
https://www.hifishark.com/model/canton-ct-120
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