Keyboard malfunction progression: first ED, then FG, now T
The entire top case assembly controls the physical mounting as well as the electrical connection. I would see if you need battery service for it and pay for that repair. Get two problems fixed for the same cost.
Without removing the battery, it may be hard to know if this is liquid damage / corrosion or mechanical issues like grit or just physical parts wearing / breaking or it's electrical connection on the USB bus. Also, a battery that expands could cause all the issues and need service.
I would get a quote for repair and then wait till you can't use external / bluetooth keyboard and they pay for a repair if it's not covered by Apple. Sometimes Apple extends coverage for batteries and keyboards, so it doesn't hurt to ask for a quote - sometimes the price comes back zero.