On one of the coldest mornings here--probably -15 F--I started my car as usual, but had driven only 1/8 mile, and was traveling at 25mph when I heard a slight "clunk-clunk" and the car lost power to the drivetrain. Drive and 3rd gear were both gone. 1,2 and reverse still functional. The transmission is a 4speed automatic (apparently one of the first "4EAT's", the car is older, but has very low mileage, has never been abused or driven "enthusiastically", as they say on the Subaru web site. I was told that this sounded like a a "sensor" problem, but it turned out to be a more major failure than that. Does this happen a lot? What is the expected lifespan of this transmission?