Super A mystery

I backed my tractor into my garage, to find this line of oil from the rear axle pan. Looking closer, I find this 'slash' in the pan, and upon pulling the pan, found this washer sitting loose in the pan. I've been driving this tractor for a year. All I can guess is that this has been sitting in the pan from a previous repair, unnoticed by the mechanic at the time, until the edge finally caught a cog on the bull gear. Hard to believe it's migrated from somewhere else.
Anyone have an idea, given the shoulder on the washer as seen in the plane view, what specific purpose it might have served, to help identify from where it came?

Al

Here's the washer-

scotty

Thanks for the replies, guys. This forum is awesome.

Hugh, the inner diameter is 1 3/8 inches, but I can't 'see' the axle to measure it.

I took the pan to some local guys and got it welded, after beating it back into shape. LOL, they told me that washer BELONGS in the pan, it keeps the oil stirred up! Comedians! LOL

I took off the inner axle cover, and I believe I see the washer hard up against the bearing. Guy must have just replaced it when he "lost" the original. I guess I'M lucky it finally jammed when I wasn't mowing, when I wouldn't have noticed it in quite a while. How he didn't know where he dropped it is beyond me. You'd have to know it would cause havoc sooner or later, landing in the pan. A magnet could have retrieved it pretty easy.

Can I ask the next question to which this leads? That bolt must screw INTO the axle. When I put a wrench on it, it wasn't loose, but it wasn't tight, so I wondered if it was used to take up the bearing tolerance, but then there's nothing to hold it from loosening, and I would have sooner expected a castellated nut and a cotter pin. Do I have this wrong? Do you use that lug-ed spacer to set the tolerance, and then turn this bolt down tight?
Oddly, my parts-manual doesn't show this bolt at all, nor one of these washers on the other side. Makes it hard to tell what's supposed to be where.

Again, my appreciation.

I was just telling you what I remembered, and that was the reason I stopped where I did. I have a feeling there is more than one washer on that axle assembly. You may indeed have a washer missing in there next to the bull gear. Just could be the reason why that bolt in end of axle was not excessively tight. You have a consultation with scotty or banjo.