Just adding what i got from Lego. Theyre saying its an actuator problem..
Thank you for getting in touch with us.
First let me apologize for the difficulty you've had so far with your new 8043 Motorized Excavator.
Our design team recently became aware of this issue and removed the item from our LEGO.com shop.
We're now working really hard to redesign the linear actuator - the source of these motor problems! We expect to have a solution up and ready within a few weeks.
If you would prefer a refund or exchange for the set this can be arranged, but we would love to see your set completed and fully functioning. Since you've asked I'm going to put you on our list for those replacement actuator arms to save you from having to get back in touch with us. However, if this isn't enough and you would rather get a refund or discuss the issue further with us please use your reference number XXXXXXXXXX and reply to this email - or give us a call and we will come up with a solution that works for you!
If you do decide to wait for the replacements it shouldn't be more than a few weeks before you get that actuator in the mail; and as I mentioned before, you're already on the list to receive these replacements.
Happy building!