dude "tranny warning only came on once" Once is wayyy too much when your talking a tranny fault.

However I do not think your rough idle or CEL is due to this-CEL is an emissions relate warning light--so anything that changes or screws up the amount of emissions gases beyond a certain level--so spark plugs, coils, any drivetrain pieces, cylinder misfires, o2 sensors, gas cap open--did you check your gas gap is properly closed?

Rough idle could be rom lack of driving it more than anything---

Lots of things but nonetheless your tranny is probably fine--for now. You DEFINETLY shortened the life of it that is a no brainer--I would be getting an extended warranty that is forsure from someone as this tranny will fail--just a matter of if it is you or the guy you sell the car to this year to avoide having to pay for that 10k damage

 

The same thing happened to me. I took the car in for a check-up, and the dealer told me the tranny fluid has a minor leak. It was priced at $500 bucks with labor. At first I was like NAAAA I'm good, but then it ate away at my mind of tranny damage, and I went ahead and fixed it. Now no worries, and some warranty. Sooooo with that being said your a fool to let it go so long. Don't take it the wrong way, but with these cars you want to be on top of everything.

 

Your looking at 7,500 for tranny not including labor .

 

You can get a used tranny for half of that if you look around-plenty out there from multiple vehicles--but I am afraid this is a 10k dollar repair if you want to use OEM--even bmw will try to replace it with a remanufactured unit which probably will run 5k USD without labor.

I would say 7500..