With no prior indication of any transmission problems, after picking up my 94 E420 after having a tune up, I started noticing a chemical smoky smell once I parked the car. The smoke would be coming from the space between the hood and windshield. There was liquid leaking onto the parking lot on the passenger side. It drove fine for about 2 days and then it quit going forward and will only go in reverse. The transmission fluid level is fine when looking at the resevoir. Any suggestions on what the possible problem is. Again, it runs perfect except for this and there was no warning whatsoever before it stopped going in drive. Thanks.