Repair old keyboard where key combinations fail, and some keys fail at startup

I have a 14-year old USB Apple keyboard that I would like to refurbish, but I have no clue how to proceed. The tab key lost its rubber dome, so I replaced it with the dome from the Caps Lock key. Each key in the keyboard works individually, but the left Command key fails to work with c and v , preventing the common use of copy-paste. Also, both Option keys fail at startup (even though they work when the computer is booted), preventing the boot into recovery mode. Is it possible to diagnose and repair such a keyboard? Update I opened the keyboard following and here is a picture, showing clear s

Question by ginjaemocoes on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.