Rule out the usual hiding places first. If the piece really is gone, check the set piece by piece
and leave with the element ID LEGO asks for, or a link to buy the part.
Technic Brick 1 x 2 [1 Pin Hole]WhitePart 3700Element 6619284 or 370001×4
Windows and Doors
4 pieces
Window 1 x 2 x 2 Flat FrontReddish BrownPart 60592Element 6382102 or 4595814×4
Technic Connectors
2 pieces
Technic Pin Connector Hub with 2 Perpendicular AxlesBlackPart 10197Element 6099801 or 6098801×2
Transportation - Land
2 pieces
Mudguard 2 x 4 with 2 x 2 Studs and Flared WingsBlackPart 41854Element 4184813 or 4163939×2
Tools
1 piece
Brick and Axle Separator v2.0OrangePart 96874Element 6240515 or 4654448×1
Tick each piece as you find it, or mark it missing.
When a piece really is missing
Ask LEGO
LEGO takes requests for pieces missing from a new set through its customer service site. The form asks for
the set number and each piece's element ID, the number printed beside the piece in the parts list at the back
of the instructions. This checker lists both.
Mark a piece missing and your list links it to an eBay search for that part, which also covers pieces from
older or second-hand sets.
Keep a record
Copy or download your missing list (the CSV opens in any spreadsheet), or print the whole checklist and tick
pieces off on paper. Your marks stay in this browser, so you can check a big set over several sittings.