M4300 8X8F stack ports down

Hello.

We have 2 M4300-8X8F switches in stack mode. Stacking ports are port 7 and 8 respectively. Since a few days port 8 is dead on both sides. Sometimes I could observe a link flap on these ports. I do not want to unstack and restack. What can I do, swap the Cu modules used? Is there a way to check the switch port?

Andreas