I have had many, if not hundreds of these machines apart fellas, and what I have found that causes this problem is one of three things. One, when Whirlpool built these machines at the factory, the tub ring didn't get snapped on correctly around the complete circumference of the top of the tub. I think that there are 8 points(might even be 10). When you carefully pry up on each of these tabs to take the ring off, you might have seen how flimsy the plastic material is for the tub. So if they don't all get snapped down correctly, OOPS! The plastic gets distorted. There isn't much room between the tub and the basket if the first place, but if you have ever spun one of these machines with the cabinet and the tub ring off, you will see that it's a pretty close fit.
The next thing I have found is, say a customer needs to move the machine away from a wall or similar situation. They simply open the lid, grab what they believe to be a solid spot inside the machine (which sometimes ends up to be the tub ring and not the cabinet of the machine) and drag it away from the wall or wherever. OOPS here we go again. Remember those little tabs we talked about earlier? This time you have everything together and it would be pretty easy to miss partially pulling the tub ring out of it's correct position.
The third and final thing, although I haven't seen it for a long time, is a bad balance ring on the top of the basket. If you remember some of the first Design 2000 DD machines that came out in 1981, those balance rings for the basket were notorious for the ballast leaking out of them and were entirely different in appearance(They were actually stamped as part of the basket). There was a plug on the outside of the basket that would come loose over a period of time, and sometimes rub the outside of the tub during spin. Once all the ballast leaked out, OOPS! Now you have this thing jumping all over the place. Remember that tub ring on the top I was talking about? Well, same rules apply here too. Needless to say, I don't see how anyone could use the machine in a condition like this. Noisy, jumping all over the joint, things like this. Personally, I feel there is no excuse why all of these machines cannot be smooth and quiet, given the fact parts are pretty inexpensive and easy to get. But then again, most people just toss their stuff in the machine and go. Plain and simple they don't care(guess that's why guys like us have our fun). The balance ring for the basket on the later machines is permanently installed around the top of the piece, but I have still seen a few of them come loose. Even though it doesn't seem to cause an out of balance condition in some cases, the ring is still loose, and being a bit tight between the basket and tub, what movement is there under certain conditions at 680 RPM I would say could cause it to rub this hole in the tub.