fwiw, the former owner of Rennlist started his own forum after he sold Rennlist to Internet Brands. It's called Reutterwerk.com
It's a bit slower with traffic but it also has a Bimmer section, too.
Otherwise, yeah, Rennlist or Pelican Parts Technical BBS forums are the best. You don't have to buy a membership to RL to post and read. But you won't get to use the classifieds. A paid membership made more sense when John and Jen owned the site, but now it's corporate owned and there are more ads and sponsors.
And also agree that Planet 9 is the best for the Cayman specifically.