I was saying to use the Hondabond instead of the gasket when you do remove the cover. As far as removing the cover while in the car never personally done it, but I would say to read this
http://mazdatrix.com/faq/pulley.htm .
Use a block of wood to hold down the clutch, radiator fan out depending on clearance, belts off, main pulley off, clutch in at all time from here until the main nut is re-installed, undo nut, pull off the hub (make sure key stays in), pry out old seal don't scratch anything. Use a block of wood or a socket and tap new seal in, install hub and torque down and then install is reverse of removal. Just an idea of what is going to be done. Make sure you read the Mazdatrix faq above.