All major seals leak on 2000 Chevy?

I got an oil change at Jiffy Lube about a month ago and they reported that "all seals leak: Major" and they had no read on the oil level when i brought it in. What parts, gaskets and seals do i need in order to fix this. I have tools and an engine hoist and a dad to help me do it all but I need to know what I need to buy before I pull anything out. I have a 2000 Chevrolet Silverado 1500 Z71 LS 5.3 Liter V-8. Its an automatic transmission too. Thanks :D