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Sounds like you need a new drive. You can try disassembling it and cleaning the lens. There's probably a guide out there. Perhaps clean and lube the mechanism which moves the laser.

As long as it's slot loading. A drive which fits should be pretty cheap. Although I think rev a is tray loading.
 
Sounds like you need a new drive. You can try disassembling it and cleaning the lens. There's probably a guide out there. Perhaps clean and lube the mechanism which moves the laser.

As long as it's slot loading. A drive which fits should be pretty cheap. Although I think rev a is tray loading.
It is tray loading, but I have another one that is slot loading that is running Mac OS 8.6 and it does read CDs
 
I always had to clean the lens with a compact disk that had a bristle and a dab of lotion.
off topic, are you still doing fun things on the iMac?
 
It is tray loading, but I have another one that is slot loading that is running Mac OS 8.6 and it does read CDs

You can take the drive out and put it in an external enclosure. Then install the OS from the other iMac. Then put it back.

If you have an external drive already. You can install the OS from the other iMac to the external. Then connect to your iMac and clone it (OS X) or simply copy everything over and bless the System Folder (OS 8/9).
 
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