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.