leaky valve covers.. decent size leak(s)
If you do as dgc333 says you will not have any problem's or headaches.
the gaskets he telling you about are the best and I use the MP ones about 16-18$ but you can use them over and over with not leaks if the covers are straight and not dimpled where the bolts go in.
stay away from the cheap ones covers at $20 and chrome you get what you pay for as stated in early post.