Thanks for all the help so far.
I've dry fired the camera 50+ times. It didn't affect the light metering, but the film advance smoothed out even more.
Changing the ISO back and forth many times didn't change anything.
I have a test roll in it now. In auto mode it seems to be close. I figured out my manual settings with a separate light meter, and listened for how long shutter click was. I then took the same photo on Auto and the shutter was either the same or very close. So I think Auto mode works (I'll find out for sure when I develop the roll).
The meter reading in manual mode is more buggered than I originally though. While it does scale with changes in ISO and aperture, it doesn't change based on how much light it is getting (mostly). If the lens cap is on, it reports nothing, with the cap off it reports the same light reading no matter how bright or dark the scene/subject I point it at are. The secondary mirror behind the main mirror is definitely hanging down in what appears to be the proper position.
The secondary mirror illuminates the same sensor as the one for OTH metering so something strange is happening. The ISO dial is in common as well.
How can you tell the secondary mirror is ok do you have a dental mirror under the main mirror?
In spot mode does the light reading vary as you track the spot across a light source?
In spot mode, the meter doesn't change. I haven't swept a flashlight across it, but I have swet the camera from looking out a bright window to a dark wall, and the meter stayed constant.
It is possible the secondary mirror isn't in the exact spot, but it is hanging down very close to vertical. I can see it by looking directly at the primary mirror. You can see it's pattern back through the mirror - which upon reflection sounds like it may not be hanging far enough back, because it should be reflecting that light down, not straight back at me...
You mentioned zippo fluid on the hinges. I don't have lighter fluid around, but would kerosene work as well? I'm guessing I'm just looking for a powerful solvent?
try removing lens and shining flash light under primary mirror if on and off causes big changes in meter it most likely is mirror.
kerosene is excellent solvent but removing it mission impossible sorry Zippo will flash off but still may stain rear of mirror dont worry we are not going to clean any mirror surfaces... big sin
invest in a can or borrow. spill 1cm of Zippo into cassette tub. Find largest darning needle remove lens set shutter to B invert camera and fire shutter and lock with a cable release to provide access to secondary mirror pivots
Dip sharp end of needle in Zippo transfer to each mirror hinge until bored we need small droplets
then fire shutter on 125 lots of times probable lube turned to gum hopefully Zippo long term fix
repeat darning needle treatment if no effect Id not be tempted to use needle as a pry bar just keep trying
Ya-know, pouring lighter fluid on things only gives a temporary relief, then leaves a non-lubed hinge. Better to send it in to Camtech(zuiko john) and have a cla done. Wait until you have your test roll developed and printed to make sure thats is a problem, you may not even have an issue.
So, I was able to compare where the mirror hangs with where the mirror on my OM40 hangs, they hang at the same angle. I also used a flashlight to test it, and that had no effect. So it doesn't appear to be the mirror position that's at fault.
I'm curious what the test roll will show, but otherwise I'm done worrying about it. I won't CLA is, as the rest of the camera just doesn't justify that to me (if the body was in good shape I'd consider it, but the body's seen better days).
Thanks for all the insight guys.
Please look at the secondary mirror both cameras when they are both on B.