What is the legal position in terms of the principle of unjust enrichment......when for example

• A neighbor gets sick and goes to hospital and the friendly neighbor (AX) helps them look after their car by going into the garage and using the key given to them (for emergency purposes) and turns the car over to keep the battery operational, (AX) pays to put petrol in the car, but the car has some mechanical issue and breaks down, (AX) then takes it to a garage and pays $400 for the repair.

The ill neighbor wakes up after 2-3 weeks hospital care and is asked by the friendly neighbor (AX) to pay $450 towards the care and repair of their car.

The ill neighbor says , Im not paying anything