Its a dealbreaker for me, but try poking around other members to see where they're at, maybe there is someone salvageable.

At this conjuction of time, any org that sees China as imperialist is a joke and has to be considered reactionary.

Yeah thats a red flag... and not the good kind. Write a speech denouncing them for falling into idealism and imperialist propaganda.

Depends. I'd think like this:

• Is it a big party, with some marxist and some soc-dems etc.? Try to find like-minded comrades and use it as a way to agitate for and educate about marxist politics (if that is possible within the structure)
• Is it a small cadre party? If so you might want to skip out
• Is it a specific issue group? See if you can work in a positive way about the specific issue and discuss the topic amicably if it shows up. BUT this depens a lot on the situation!

If you are unsure, discuss with a comrade you know, write a journal, and go with your gut feeling, and don't attach yourself too much to something you are skeptical of.