Where does the oil go in my Juki DDL-5550n-7 sewing machine? I lost the manual and I don't want to buy a new one just for this one thing. Thanks.

See the error code list and remedial actions on this page

drive01_error.pdf (juki.co.jp)

There is a problem with the motor. Check your connections of wiring and such to make sure they are secure. The problem might be the brushes or might be the circuit board to the motor. Look for signs of damage or wear on that main circuit board. If found, replace the board. If the problem is not then resolved, you might contact Juki customer support. This is not an inexpensive machine. https://jukiamericas.com/pages/support

https://www.citysewingmachine.com/products/juki-ddl-5550n-7-lockstitch-machine-setup-on-table-servo-motor-stand.html

https://www.manualslib.com/manual/940610/Juki-Ddl-5550n-7.html

JUKI DDL 5550N 7 Instruction Manual

indicates a problem motor or motor control problem due to heat from current (power) usage
take it in for a service and proper diagnosis

Perhaps it would be best to contact Juki Support.

Problem with Juki DDL 5550N 7 Sewing Machine Error Code E24

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JUKI DDL 5550N Handbook

Again: JUKI DDL 5550N Manuals

Juki DDL 5550N 7 DDL550 7 Instructions Manual

http://www.atlaslevy.com/Juki-DDL-5550N-7-DDL550-7-Instructions-Manual-_p_865.html

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JUKI DDL 5550N Manuals

just add oil and clean junk off take up pump filter. no need to change oil there no combustion like a gas engine.