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.
Large Figure Head Connector Block (Toa Metru)Dark Bluish GrayPart 47312Element 4278473 or 4217832×1
Technic Axle 8 with StopDark Bluish GrayPart 55013Element 4499858×2
Technic Axle and Pin Connector 2 x 7 with Two Ball Joint SocketsDark Bluish GrayPart 50898Element 4242036×2
Technic Beam 1 x 2 ThinDark Bluish GrayPart 41677Element 6338422 or 4210980×1
Technic Beam 1 x 3 ThinDark Bluish GrayPart 6632Element 6632199 or 6364452×2
Technic Pin 3/4Dark Bluish GrayPart 32002Element 32002199 or 42110501 spare in the box×2
Pearl Dark Gray
8 pieces
Arm Mechanical with Clip [Thin Support]Pearl Dark GrayPart 53989Element 4294997×8
Trans-Neon Green
1 piece
Large Figure Head Connector Block Eye/Brain Stalk (Toa Metru)Trans-Neon GreenPart 47313Element 4238920 or 4218955×1
White
1 piece
Technic Axle and Pin Connector Angled #6 - 90°WhitePart 32014Element 6450588 or 6268926×1
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.