If this is a new smoker still under warranty you should call MB customer service. I've had my MES 30 Gen 1 for over 3 years and it doesn't leak smoke from the door seals--even with carbon buildup on the front of the smoker where the door seals close on the smoker body. I've read other posts by guys who's new smokers leaked smoke so this can be a problem with new MES units.
I wonder if the owners manual says not to use wood chunks because they give off more flame and heat smoke than wood chips? I think there's a possibility that long term use of wood chunks could damage the heating element but I'm no expert on this. But here's a warning from a Brinkmann electric smoker owner's manual: NOTE: Do not place the flavoring wood directly on the electric element. This could cause flame flare-up and failure of the electric element.
So, I was right about the flame thing. I advise buying an
AMNPS from Todd Johnson and sticking to wood pellets. Despite what some critics say here that pellet tray produces steady, adequate smoke over 11 hours or so. There's an issue using it in some of the original MES Gen 2 models, though.