Intermittent ertyuio keys on MacBook Pro

MacBook Pro 15” mid-2012 backlit keyboard, not retina

It has been a frustrating time with my keyboard. The ertyuio keys stop working. If I run my fingers back and forth across that row of keys they work again for a short while. Sometimes if I hold the failing key down very lightly and wait, the key will suddenly work. I read about so many possible solutions, but nothing seemed work. I have adjusted the Key Repeat rate, etc., set up other keyboards, such as British and tried whatever I could think of that might affect the keyboard.

I have made some major changes and after each the keyboard seemed to behave for even up to a few days, leading me to think I had finally resolved the issue. These have been done one by one and have included:

1. Log in on a separate Admin account and discovered the issue is not confined to my regular account
2. Upgrade to MacOS Mojave
3. Restart in Recovery Mode and reinstall a fresh OS that has not been upgraded for years and years
4. Order a new Keyboard
5. Open the computer up, dismantle everything and clean behind the keyboard (I have not yet removed the keyboard as this is a huge job I reserve for a future replacement step)
6. Cancelled new keyboard order because everything was working
7. Buy and install a new battery (I read that aging batteries can swell and affect the keyboard and trackpad (I could press on certain parts of the right side of the computer to get a key to work)
8. Buy and install a 1 TB SSD and RAM (from 8 MBs to 16 MBs, I highly recommend doing these two upgrades to extend the life of an older machine)
9. Reorder keyboard (returned to seller by Canada Post due to rotating strikes and service disruptions)

I am not convinced that this is a hardware problem. It could still be a software issue. When I installed the SSD, I decided to rebuild my system from a fresh OS install. The keyboard seemed to be working fine, so I began copying from the replaced HD which I installed in an external enclosure. At some point the problem appeared again, however, I can’t identify what I copied over that may be the culprit because I copied batches of files, including Library files. It would have been impossible to go one file at a time and, since the problem is intermittent and transient, testing is impossible.

Writing this has been challenging. Sometimes the keys worked, but most of the time they did not. It is only the keys I mentioned above that are affected.

Help!!! I don’t want to replace the keyboard if I don’t have to.