I'm pretty sure that your problem is down to a cracked spray arm ferrule. It's a common part know to fail and costs under £10 direct from AEG. It looks like a little white plastic ring with two plastic lugs. Although this may not be the exact part for your particular machine here is an example of what you probably need to buy:
https://shop.aeg.co.uk/dishwashers/dishwashers/spray-arms/dishwasher-upper-spray-arm-ferrule/p/1524355102
Rupert
March 2020