What could this be?

Just about finished with the bronco, and began filling the radiator only to find water leaking through the timing cover gasket. Engine hasn't ran for a couple years so I figured something like this was going to happen. when I removed the timing cover I noticed something I've never seen before. On the crankshaft in front of the lower timing gear there was some sort of guard looking thing keyed to the shaft. Looks to gotten ran over some how by the timing chain. Its very thin metal, perfect circle about the size of a half dollar. Talked to a friend he thinks its there to prevent oil from splashing directly on the front main seal? What is it? By the way I have a 77' 302. Thanks

Just a oil slinger. There usually there until someone forgets to reinstall them.

You don't need it. Ford quit putting them on at some point.