I have to say to a new owner that following the recommended maintenance schedule 30k/15k is the best thing you can do for your car. At 150K you would be due for the major service. For that trans to fail at that mileage indicates the previous owner likely didn't have most if any of the services done. You should seriously consider doing it and then staying on schedule. A well cared for older/ higher mileage Benz is an investment. A poorly cared for higher mileage Benz is a money pit.