Intermittent keyboard problem - what part to replace 1st?

PowerBook G4 17” HiRes 1.67 Ghz processor

Having intermittent keyboard problems. Seems to be getting worse. First noticed it with Command combos - such as Command-Tab for viewing open apps. After a restart, or off, and later start, often works perfectly for a while, but lately that time has diminished from 24 hours to a few minutes.

Symptoms: Combo-key presses don’t work (Cmd, Shift, Opt, Ctrl); CAPS LOCK lights for a few seconds, but then spontaneously goes off. Single keystrokes may not register at all, may register if you wait - press - wait - press another ... ; or may register and repeat 2,3 or sometimes more times. The DELETE key does the same. It may not register, or it may delelte one or more letters with one stroke.

I replaced hard drive a few weeks ago, and started noticiing problem after that. Read the Germain/Mayer post about connection beneath memory module, so confirmed that connection. Worked for a few hours. But began recurring. Tried again. Recurrence.

So went deeper and pulled trackpad ribbon off and checked keyboard ribbon connection beneath that. It appeared that the retaining flap was loose when I got there, so I learned how it worked, reconnected it and made sure retaining flap was in down position.

Put it all back together and it worked perfectly for about 15 minutes ... then same problems

So - looks like problem could be in a number of places. How do I know or make best guess as to which to replace?

Keyboard

Keyboard to Small trackpad/keyboard logic board

The small keyboard/track pad logic board beneath the trackpad

Small logic board to main logic board cable (the one mentioned in the post I read )

Main logic board?

What’s my best course? Likely to be keyboard, so replace for about $100 from iFixIt, or send to Apple because may just as well be small logic board or main logic board? (out of warranty)

Thanks for any help / suggestions.