You are correct. "Several accounts" would be accurate. Several coaches would be accurate. Since we are talking about 10's of thousands of coaches the likelihood that the disk is the issue is so small as to be simply discounted.
The OP does not indicate he has a new coach so it would be very surprising that this disk did not appear in the last 3 years. Additionally, he indicates that he cannot tell if the valve is open or not. Of all the things to check, the valve would be number one and a disk blockage somewhere WAY down the line.
No one burst my bubble. You can't burst right! Gene got it right. I tend to be correct and I would guess that I am correct in this case as well.
