Mirror occasionally sticks up

I have an old analog MAMIYA camera. I’m not sure about the exact model as it is not listed anywhere on the device (picture included). Recently the mirror started sticking in the up position occasionally. It’s usually fixed by pulling the loading arm and letting it flick back.

I’ve found some similar issues online. It’s often stated that a foam ring around the focus window is too sticky. Unfortunately, my device doesn’t have this ring.

After finicking about everything seems to work properly now, but I can bet the thing will jam again as soon as I put a new roll in it.

A local camera salesman said there could be some sticky things inside the mechanism but couldn’t give me any details.

I am not too afraid to open the thing up and inspect the insides as similar cameras go for about €20,- (so ruining it would not be the end of the world). I would like to know what to look for before doing so though.

Any ideas about where this problem could arise from?

Edit: Did a google. The model seems to be a 1964 MAMIYA PRISMAT CP (probably)