Interesting question. I hope others with more experience respond. My recent experience was with the large trunk panel and a headlight bucket. Both were purchased from Mercedes directly. Both were black.
I had read that to test the coating use Acetone and rub hard. If the coating comes off it’s not ecoat. If the coating does not come off it’s probably ecoat and can remain.
The acetone test on the trunk panel did not remove any black finish. The acetone test on the headlight bucket was quite different as it did remove the black. Both came from Mercedes.
The panels will get epoxy over them but I will scuff the trunk panel and will completely remove the black from the headlight bucket.
