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]BlackPart 3700Element 370026×8
Technic Brick 1 x 1 with Axle HoleSand GreenPart 73230Element 6359069×8
Technic Pins
14 pieces
Technic Pin with Friction Ridges Lengthwise with No Center SlotsBlackPart 61332Element 62798751 spare in the box×2
Technic Axle Pin with Friction Ridges LengthwiseBluePart 43093Element 4309323 or 4206482×12
Bricks Wedged
12 pieces
Brick Wedged, Curved 2 x 2 with Stud NotchesDark BrownPart 66956Element 63089031 spare in the box×12
Minifig Headwear
12 pieces
Hat / Flat Cap, Old StyleDark BrownPart 2514Element 6501311×12
Technic Beams
6 pieces
Technic Beam 1 x 2 ThinTanPart 41677Element 6376461 or 4205392×6
Bricks Round and Cones
3 pieces
Brick Round 1 x 1 Open StudReddish BrownPart 3062bElement 4211183×3
Bricks Special
3 pieces
Brick Special 1 x 1 Studs on 4 SidesBlackPart 4733Element 473326×3
Technic Bushes
3 pieces
Technic Bush 1/2 Smooth with Axle Hole Semi-ReducedLight Bluish GrayPart 32123bElement 6271165 or 42115731 spare in the box×3
Technic Steering, Suspension and Engine
3 pieces
Technic Steering Wheel Small (3 Studs Diameter)BlackPart 2819Element 4580509 or 4160709×3
Tools
1 piece
Brick and Axle Separator v2.0Dark TurquoisePart 96874Element 6254100×1
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.