I'm not sure about the 300 / 103 motor, they fail so rarely, but a 400E is easier than an E320. I'd say 2 to 3 hours for a first timer, which is maybe an hour less than an 320. Dealer have been known to charge up to 6 hours for a 320 but I know someone who has witnessed it done in an hour and 15 minutes by an experienced tech.