Mazda Parts you can get cheaper than at the dealer thread

[PatrickGSR94]

How and when would a person know when this part requires replacement?

You'll see an oil leak around where the wire harness plugs in on top of the valve cover. I tried replacing the seal in the valve cover, but it still leaked up through the harness plug itself. I had to de-pin the harness to completely clean the oil out of everything when I replaced the valve.