Unreliable keyboard - repair or replace?

BACKGROUND: Altho nearly 8 years old, my MBP does everything I need it to as I’ve upgraded it with 8GB RAM, an SSD and a 750GB hard drive. The battery, which I replaced a couple of years ago (it was swollen and affected the trackpad) holds a charge pretty well, but the system report says it needs service. I manage with ‘Keyboard viewer’ and a bluetooth keyboard , but it’s not ideal. Nothing has been spilled in or on this Mac, and I recently removed the bottom and everything inside looks good to me.

SYMPTOMS: The first keys to become unreliable were 1, 2, 3, slowly spreading to 9. Lately the ‘E’ key only works if I hit it hard. The keyboard seems to work better when the device is cold.

QUESTION: before undertaking the ‘difficult’ Top Case replacement, I just want to check whether there are other things I should check.