Tony,
Did you notice resistance worthy of screws when you removed yours? Or not?
Mike it was VERY tight, in fact the seal seemed to have some sort of mounting paste on it that had set very hard - you can see the residue of it on the edge of the seal.
However once I really leaned on one of the screws and the seal started moving, it popped out when I moved to the next screw. I did not try prying on the seal as I could not see any way t do that without putting force on the crankshaft and I was not confident of my Heath-Robinson crank blocking effort (next time I will make a bolt and bracket.