Mirror issues

Hello,

I inherited a ricoh xr-2s from my dad (i know this is a XR7 forum, but hopefully u can help.)
the issue happened recently (at the end of my first roll of film) with about 4 shots left. The issue is the mirror comes up and stays up WHEN i advance the film to take the next picture. then i cant take a picture. i have to wind again and let the forward film lever swing back (its spring loaded), when i do that, the film gets exposed... thats when the lens isnt is, when the lens is in the camera, the only way to get the mirror back down is by pressing the aperture preview button.. the issue isnt the battery as they are new and it even does that on the mechanical setting..
Any ideas?!? i mean this really sucks, it was working fine, then only half the time, now not at all!!
Id rather fix it on my own if possible, its an old camera and its repair will be more costly than its actual worth! but i love the thing and it has sentimental value.
Thanks alot.