My understanding is that as long as you refer to your exhaust system as a solvent trap instead of a muffler or suppressor you can keep the ATF away

I've put half a quarts worth in my truck before due to the old wives tale. I don't think it's a good idea by more. But if you are worried about out whatever is left in the transfer tube, I don't think it's remotely something I'd worry over.

ATF is just oil with a different additive package. Its fine.

Old timers used to dump it in the crankcase before an oil change because the detergents in ATF really do clean out carbon deposits.

I think the reason no one does it any more is that synthetic oil really is just that good, and modern cars aren't old farm tractors. Farm equipment might get one oil change a year, but will sit idling for hours and hours. A loose, rattly old flat head ford won't mind a bunch of carbon chunks flying around in the oil system. Your BMW probably would.


But a few ounces? I wouldn't care enough to change the oil again. It'll be just fine.