I just did the very thing you mention on a powdercoated
oil pan. The brake cleen dries so fast it doesn't have much time to soften the finish. I also used laquer thinner to wipe down the powder coating to prep for paint and yes it did soften the finish but again did not ruin it. I spray painted the pan to cover some scratches in the powder coat and while giving it a final cleaning on the inside before installing it, i dribbled some laquer thinner out the plug hole and it did leave a streak on the bottom of the now painted pan. It's an
oil pan and I'm sure it will have battle scars in no time anyway. Good luck with yours.
John