Can you use WD-40 to loosen the blades in a Mixer Grinder?
WD-40 contains naphtha, hydrodesulfurized heavy; 1,2,4-trimethyl benzene; 1,3,5-trimethyl benzene; mixed xylene isomers; and surfactant, which are not for food use. WD-40 can harm/dissolve certain plastics and rubbers (perhaps used in your blender). 

I think the toxicity of WD-40 is relatively minor, but essentially, WD-40 isn't food grade. Now, I know that this is not a food facility, but I would definitely opt for food grade mineral oil to prevent rancidity and rusting issues. FDA Code of Federal Regulations 178.3570 allows food grade mineral to be used for lubricating food processing equipment, and USP grade mineral oil happens to be the primary lubricant in the industry (I'd guess at least 90% of the lubrication is done with mineral oil). 

CFR 178.3570 also allows use of naturally-sourced fatty acids (like capric acid, caprylic acid and caproic acid, which are more for antibacterial applications, and can/will cause corrosion issues), polybutene (maybe for electronic parts), isopropyl oleate (pricey), and castor oil (which is gummy, can become rancid, and induces cramping). The petrolatum that is mentioned is USP grade (CAS Number: 8009-03-8) which is basically vaseline; and it is only for use in "as a protective coating of the surfaces of metal or wood tanks used in fermentation process". The rest of the lubricants that are mentioned in CFR 178.3570 are not actually lubricants (more like, antibiotic soaps and chealating agents) or are simply exotic materials (even for industrial manufacturers).

So, what I'm saying (to be 100% clear) is that USP mineral oil is the only realistic lubricant allowed by FDA. Isopropyl oleate would be my second choice, but the price is going to be about 10 fold higher than mineral oil, and castor oil would be my third choice for reasons mentioned above. The rest of the "lubricants" are basically industrial-use lubricant additives (used in very minor amounts for more specific applications).