i think it might be the longest running live action sitcom.

Always Sunny? AFAIK it is. Seinfeld only got 7 seasons IIRC, and most of the "classic" sitcoms got even less than that.

I just wanted to point out that even stuff from the 90s was still getting that treatment, even if it's more because Seinfeld reruns were a common part of the afternoon block on broadcast stations during the 2000s than because of people having seen them when they were new. In comparison Cheers was late night filler along with Married, With Children whenever I saw it show up somewhere.