Hi. My name is*****'m a camera repair technician with over 20 years in the business and I'll be glad to help you with your question today.
This sounds like a shutter issue to me. They do go bad all the time and require replacement. However, Canon, in it's infinite wisdom, has discontinued support for the 50D. This means they no longer repair them or sell parts for them. There is a limited and dwindling supply and when they are gone, they're gone. Have you considered upgrading to a newer model?