I had to replace mine about a month ago also. I guess I was lucky, but I used 3 different size screwdrivers, smallest to largest working them side to side gently. I was very careful not to damage the casing. It took about 15 minutes of tedious work, but it finally broke free.
Then I did used a soft rubber hammer to put the new one on, that dowel is a pain. Don't forget to replace the gasket too. It was such an accomplishment getting the cover off, I almost forgot the gasket.