llonman, you probably should replace the crank seal as well if you are going to be in there. A new seal put in by someone who knows what there doing, has no more of a chance to start leaking then the current seal and actually has a far less chance of leaking as the miles start to add up. It never seems to fail that once you get in there and start disturbing things with wrenches and stuff, that one seal you didn't replace will be leaking 2 miles after the car is put back together
Also, if the car has close to or over 100,000 miles on it, replace the water pump if it was never done before. I've seen some pumps last much longer, and I've seen some not even make it to 100k miles, but since you will be right there and already have the T-Belt off, do it, especially since the pumps are very cheap from Subaru.