Hey! That was my first SLR camera. I went through three of them, two in one summer. The problem you described is a familiar one. I recall the aperture indexing ring got grit in between it and the body, so that it would stick when I changed apertures. It was easy enough to take apart, clean and put back together, if my memory serves me well. There were just four (screws) on the chrome plate that held the ring in place. Once those were removed, I could extract the aperture index ring. I don't recall if that had a string mechanism to engage the index or not (I did this on numerous Nikons), but think it was just a tab that needed to be properly aligned with a slot during reassembly.

The meter problem may be more significant than that; however. I recall mine doing the same thing after I tested its impact resistance with the granite on the back side of Half Dome.

Good luck!