Glenn - The thick rubber ring your screwdriver is stuck into is the "cushion", not a seal. You should go back and read the shop manual pages Bill Hanlon posted above.
They describe how to disassemble your driveshaft unit, including removal of the bearing. If you are having trouble reading the smallish pictured pages, go to the Chevy Shop Manual starting on
Page 4-52 with the instructions for the "3/4 Ton Truck Propeller Shafts".
Disassembly instructions are on page 4-53.
You might access these on your computer, if you can, and print them so you can have them right at hand while working.
