Hi there, wondering about this discoloration... I don't understand how I should trace this leak and how to tell if it's coming from within or external source, any thoughts would be much appreciated new to the disco scene... Was underneath cleaning out the oily grime and noticed this

 

I'd suspect a valve cover drip. Or, if you have a greasable drfiveshaft, excess grease flung onto it. Coolant overflow is also just above there but unlikely it would look like that.