Persistent GFCI trip by Plug-In 2014

I bought my car used in 2021. My garage wiring wasn't up to code so I didn't charge it until I could afford new wiring. After that, I noticed the GFCI would trip occasionally while charging. The frequency increased so I called the electrician, who replaced the outlet. He said the frequency increased because each fault on the circuit damages the GFCI slightly; it will trip increasingly easily as that damage increases over time. After several months, the same problem happened again. The second time the electrician replaced the outlet, he put in a dedicated 20 amp circuit for charging. He said if the problem happened again with the dedicated circuit, the problem was with the car or cable.

Guess what's happening again? The GFCI has tripped during 3 of the last 4 times I've charged the car. I might get half a charge, 75% of a charge, etc. The charging cord from the dealership appears new. I tried having the dealer troubleshoot, but all I got was a funny look; they charged the car for me, but it won't trip their breaker because I don't charge there all the time.

Does anyone have any suggestions for me to try, or to tell the dealer to try? I don't want to replace the charging outlet every year or two...