I'm not a "rc helicopter" specialist, however I am a CNC programmer/machinist. I totally think spindle oil or "sewing machine oil" as you call it would be an excellent choice. it's an extremely light hydraulic oil and would use it on my helicopters.
I recently ordered this stuff on amazon, and it made some of the bearings feel like new
I will go with Tunder man got from amazon, for helis bearing you want to use high speed non friction oil, and double check all your bearings that are not worn out, if so replace, a worn out bearing can cause glitches in your receiver and have some problems when flying. Good luck!
.