What I would suggest doing with TS12, since you already have it installed with assets from 3rd parties like JR and such, Install a fresh copy and only use it for multiplayer. Actually, if you're only going to join other people's routes and sessions, you can use the one you have. When building routes and sessions, it's good to have a copy with only builtin content and content available on the DLS, so that you don't put 3rd party content into the route/session by mistake.