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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.
Checking
11 pieces in 10 part and color combinations.
LEGO counts 10 pieces. This inventory comes from a separate parts catalog and lists 11; the two do not always count the same elements, so their totals differ. Spare parts are counted in neither figure.
Builders who report a missing piece often find it in one of these places. Tick each one off as you look.
LEGO's request form asks for the set number (7842) and each piece's element ID, both listed above.
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Duplo Panel 1 x 2 x 1 2/3 Sloped with 3 Embossed Gauges
×2
Duplo Truck Semi-Tractor Cab with Yellow Base
×1
Duplo Water Container, 2 x 3 Studs on Top
×1
Duplo Hose 11L with Stud Holder and Black Hose
×1
Duplo Siren / Flashing Light - Trans-Dark Blue
×1
Duplo Brick 2 x 4
×1
Duplo Truck Base with Molded Engine 5 x 9
×1
Duplo Hose with Flat Silver Nozzle and Stud Holder
×1
Duplo Figure with Headset and Cap Yellow, with Dark Blue Arms, and Legs, Yellow Knee Pads Print, and Yellow Vest with ID Badge and Radio, Open Mouth Print
×1
Tick each piece as you find it, or mark it missing.
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.
Request a replacement from LEGOMark 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.
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.
