Hello!
I tried again - I purchased a new PRAM battery and a new RAM slot
Performed a PRAM reset (win+alt+P+R) - doesn’t do anything
Why did you purchase a new RAM "slot"? I don't think it will help solve your issue of the Open Firmware Protection password. Of course, unless the one in your mac is damaged and needs a replacement.
The Open Firmware Protection can't be reset by resetting PRAM alone. If it was that easy, it would be too weak to be useful. In Apple's idea the Open Firmware Protection can only be reset in two occasions.
1. By the person who knows the password.
2. Or by the person who can access the internal of the Mac.
Since you don't know the password. The option 2 is your exit.
To reset Open Firmware password for a PowerPC Mac without knowing the password, follow these steps:
1. Turn off your Mac.
2. Change the amount of RAM in your Mac by removing or adding a RAM stick, or, if the Mac has only one stick installed, replacing it with another one that has different capacity. Replacing the RAM stick with a new one with the same capacity does no good, since the amount of RAM is still the same.
3. Immediately after changing the amount of RAM. Turn the Mac on and hold the Command-Option-P-R keys to reset PRAM. You need to hear the bong/chime at least three times (the video in the link below suggests four) before lifting your fingers and let it boot normally.
BTW, If, after changing the amount of RAM, you let the Mac boot normally instead of resetting PRAM, then you will have to turn it off and change the RAM's amount again.
This is a video demoing the process to reset it on an iBook G4.