I have a 1990 Rickenbacker that has had the same strings on it for 34 years.
They sound and perform as new.
I take them off and rub them with a rag soaked in 91% rubbing alcohol. Back and forth, the entire length of the string. One direction down, one direction back up. Dozens upon dozens of times, keeping the rag soaking wet as 91% evaporates quickly.
Then, and this is the important part, I polish the string to get all the residue off with a fresh clean cloth...I do it the same way, full length up and down, dozens of times.
These were generic strings with small chrome ball ends that came on a cheap chinese bass. But, they sounded UNBELIEVABLE with an aggressive LOUD midrange biting clang without being scooped or sizzly. They felt great, and SOUND great. I have found nothing comparable in over three decades.
And since I have no clue what they actually ARE, it is imperative that I keep them performing as new.
Thirty-four years later, they do. Using the method above.