I used Appliance Parts Pros and YouTube to diagnose likely causes and learn how to open the machine up. The motor coupling was cracked (it had an original all-plastic coupling) and the agitator dogs were totally obliterated. Once I saw that, it was (mostly) easy to order parts and perform the repairs. The new motor coupling had a *slightly* smaller inside diameter and I needed to scrape the metal sleeve with a small file before it would fit.