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.
LEGO counts 280 pieces. This inventory comes from a separate parts catalog and lists 284; the two do not always count the same elements, so their totals differ. Spare parts are counted in neither figure.
Before you call it missing
Builders who report a missing piece often find it in one of these places. Tick each one off as you look.
Technic Rubber Belt Medium [24mm ID] [Round Cross Section]RedPart 85544Element 4544145 or 4544143×2
Tan
6 pieces
Technic Axle Pin without Friction Ridges LengthwiseTanPart 3749Element 4666579 or 4186017×4
Technic Gear 20 Tooth BevelTanPart 32198Element 6031962 or 4514557×2
Yellow
6 pieces
Technic Bush 1/2 Smooth with Axle Hole Semi-ReducedYellowPart 32123bElement 6271167 or 32123241 spare in the box×4
Technic Rubber Belt Large [33mm ID] [Round Cross Section]YellowPart 85546Element 4544151 or 70905×2
Trans-Clear
2 pieces
Storage Bin Lid, Dacta [For New Style Trays]Trans-ClearPart 54190×1
Technic Gearbox 2 x 4 x 3 1/3Trans-ClearPart 6588Element 6507887 or 6254290×1
Trans-Green
2 pieces
Brick Round 1 x 1 Open StudTrans-GreenPart 3062bElement 6514234 or 6238046×2
Trans-Red
2 pieces
Brick Round 1 x 1 Open StudTrans-RedPart 3062bElement 6514235 or 6238673×2
Trans-Yellow
2 pieces
Brick Round 1 x 1 Open StudTrans-YellowPart 3062bElement 6514236 or 6238674×2
Blue
1 piece
Storage Bin, Dacta, Small [New Style]BluePart 900581×1
Orange
1 piece
Brick and Axle Separator v2.0OrangePart 96874Element 6240515 or 4654448×1
[No Color/Any Color]
1 piece
Sticker Sheet for Set 45300-1[No Color/Any Color]Part 45300Element 6138763×1
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.