The "electrical fire" odor you smell is most likely ozone, generated by the natural arcing of the brushes as they slide across the commutator. Said arcing can become noticeably worse over time, primarily due to age-related degradation of the capacitor(s) designed to reduce it, but also general brush wear and fouling. As for the noises, they could also be caused by said brush issues, or just general grime causing internal parts to stick, its hard to say for certain. A good internal cleaning is always a great place to start.

Thankfully, capacitor replacements tend to be pretty straightforwards, swap with the same value, though in the case of Mixmasters you'll probably have to jury rig your replacement into the old capacitor's body, so it'll mount on the proprietary internal assembly. Digikey is the source I personally use, they have a wide selection and good quality control so you don't get burned by fake knockoffs.

Food safe grease isn't a *bad* idea, but its not 100% required. They have contained "standard" non-safe grease, for decades of hard use, and most leakage you see has occurred extremely slowly past felt or cork seals, rather than from service. It depends on how confident you feel about it, I suppose.