"So I bought this set thinking it would be the MOST perfect Lego set I’ve ever built for the money (great building experience, awesome play functions, and best of all, no stickers!), and it comes pretty close, except for one problem. On mine, the gearbox made a grinding sound in lower gears when you roll it—not smooth at all. So, being the perfectionist that I am, I ended up taking the whole thing apart and tried to fix it, only to run into the same problem. It appears that by itself, the gearbox’s gears rotate smoothly, but once I connect it to the rear differential and connect the wheels to the gearbox, rolling the wheels cause friction and the gears to grind and “jump”. So ever since I’ve taken it apart, I have rebuilt the gearbox about eight times—following the directions to a tee— and still haven’t solved the problem and the model is still in pieces as I write this review. I’ve reached out online and people have told me that this isn’t normal and I even contacted LEGO support and I’m still waiting on their response after sending them video and photos. I’ve built the Bugatti Chiron a couple months ago and that thing rolls as smooth as butter. I was hoping the Sian would be the same and ever better, but at least mine isn’t. I can only hope LEGO support can help me find a solution to help my model work like how the designer intended, and if that ever happens, then this kit is absolutely perfect."