You have 3 10mm nuts securing the motor, if it's the first motor you need to remove the rubber sleeve
that connects the exhaust to the second motor.
There are 3 wires, the earth is obviously green, the other 2 wires are interchangable so cannot be fitted
wrong, so not necessary to mark them.
Remove the wiring connectors from the motor and replace on the new motor.
It is very simple, just take your time if it's the first time you've done one.
As to the heater they are prone to a slight leak around the seal where it's attached.
I don't know about now, but they used to be standard Haden kettle elements, which is what i used.
seal it with silicone sealant. It may even be the kettle plug worn.