Washing machine not agitating (very loud)
I had a similar issue with an LG. If the basket is overloaded too often, the weight stops the agitator spinning and it eventually strips out the plastic teeth inside, especially when it flips back and forth. I'd imagine it's a design decision and saves on repair costs. 

The metal teeth still look in good shape from what I can see. It looks like you probably need part W10609480.

When assembling the washer again, clean the bolt with a wire brush or similar and use a little blue Loctite to stop itself working loose.