While I really like Mudslinger, he's the one with the actual design defect. I'm on my 3rd Mudslinger due to the legs cracking in half when in his "powered up" mode. Here's a close up image of the crack.
I originally thought Double Clutch was a piece of crap (and I still don't like the vehicle drone concept), but he wasn't as bad once I took a deep breath and carefully went through each step of the instructions. After I did that, I was able to get his powered mode's chest to sit properly with the pegs and everything connect together properly. The only remaining design flaw I could see was how the connectors for his arms were angled.
Browning, Dai Atlas and the Big Powered Giftset, Galaxy Shuttle, Guard City, Battle Gaia, Marlboro Wheeljack, + more!