The key is to replace the LIM gasgets before they let loose and do damage. If the inside of your oil cap has filmy oil that looks kinda like light brown butter, it'* definitely time. if you find antifreeze in the oil when you change it, it'* definitely past time.
Doing the work yourself is fine and not the difficult as long as you are skilled and know you're way around a motor. Here'* a thread on changing a LIM http://www.gmforum.com/t278911/
You can change your valve cover gaskets now or when you change your LIM. It'* up to you.