My 550 touch screen gave up recently after 5 years. Following the directions in this thread I had little problem getting it to work again. I ordered this part
from ebay. The cost was $21, which included the freight. It was the exact correct part and arrived quickly (from China) via FedX,
The only problem I had was when I over tightened a screw and striped out the head of said screw. I guess I will never learn. As stated by others the response of the new touch screen is much faster than the original.
Thanks to the posters of these directions.