Dishwashers (and most appliances) are now made to break after a few years. If you want to fix it and learn a lot in the process, I have had good experiences with Appliance Parts Pros. There are exploded views of every appliance, and when you click on the part you need there is usually an installation video.

At my old apartment there was a really crappy dishwasher that always had standing water at the end of the cycle, which then turned moldy. I asked a neighbor and they had the same issue. I took it apart and attempted to fix the problem, to no avail. After doing that watching a lot of repair videos I’m pretty sure standing water was an intentional feature, probably because it was cheaper than making an actually useful appliance.