We use our broiler a lot (several times a week) and some foods splatter grease on the element. Does grease deteriorate the element over time?
Probably a little over time but is not something I would worry about.
The elements are the same type as the ones used in dishwashers and electric barbecues so are pretty robust.
Thanks for the reply denman! 
The reason I ask this is that I’m replacing my broiler element because it started to spark and burn yellow. I noticed that there were four pit marks in the element on one side with melted metal fragments stuck on it.
I assume then that since this unit is over 17 years old elements evenually wear out and this is just a case of a worn out element?
[quote=denman;82580]Probably a little over time but is not something I would worry about.
The elements are the same type as the ones used in dishwashers and electric barbecues so are pretty robust.[/quote]
Yes, that is what it sounds like.
If the heating wire inside the element get a crack across or the elements coating, it will act like an arc welder till the gap is large enough that the voltage cannot jump it.