Minolta XG2 problem

The mirror on my XG2 has an intermittent problem in that after the shutter is released, the mirror stays up until I gently move the advance lever. Any idea what's happening and if it's easily repairable?

I've also seen this happen due to bad/gummy foam rubber used for the mirror bumper. Easy to check and to replace. Often will leave residue on the edge of the mirror.