Replacing outer crank seal & Timing Belt....

I have a 1995 Lumina, its continually leaking oil from the outer crank seal behind the pully, how much of a problem is it to replace that seal and gasket?

Replacing the crank seal takes about an hour. However, I'd check the front cover and make sure the gasket is not leaking, especially above the oil filter housing. I've has two that leaked at the same area. Good Luck.