Whew, okay... The GRIIIx cleaning process didn't exactly go as planned, but was still a success overall. I followed
this guide which was succinct and had all of the necessary info to get to the sensor in a safe way.
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You can barely see, but there is a bit of dust sealing around the gap in the top plate for the shutter button.
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LCD panel is extremely slim and sealed to the back of the camera.
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This is the final hurdle, and proved to be a bit of a problem for me. There are three silver screws which need to be removed in order to separate the sensor assembly from the lens assembly and the front of the camera. One's on the top left, one is in the bottom center, and the third is hidden behind the dark gray ribbon at top right.
The issue with these screws is that they are very positively seated and have springs underneath which exert a lot of tension in order to keep the sensor assembly anchored firmly. This means they're hell to loosen. I stripped a couple of 00 Phillips head screwdrivers and desperately tried to avoid stripping the screws themselves. Eventually got the bottom and left ones free, but the right-hand screw started to strip, and got to the point where I knew it would only get worse. It just wasn't going to happen, even after I went out and got a better screwdriver set.
However, the other two screws came out, and the springs underneath pushed the sensor unit up high enough that there was a decent gap. Not enough for me to actually see the sensor, but enough for me to get a canned air straw in and blast the sensor and rear lens element (very carefully/gently). That was all I could do, so I then put it back together.
I think it mostly did the trick, however. At f16 I can still see some tiny specks, but they wouldn't show up in photos at all and aren't visible at more open aperture values. This is the before, with the biggest new monster speck and others:
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And here is the after shot:
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I used two different monitors to provide the white backlight, thus the color difference - actually, the first one was in the camera's B&W mode. the second shot is at f10, the f16 version was barely any different.
All in all, I guess it went as well as could be expected. But I do hate projects where literally the last screw strips or won't budge...