Saw a Sharp Carousel microwave last week, still working perfectly. our family had one circa 1977, the Carousel convection microwave, with 2 mechanical timers and a separate power level and temperature setting for the built in convection oven that formed the top of the microwave cavity.
it's failure mode was the self cleaning inside of the cavity, where the self cleaning top ( and the convection fan impeller) were made from steel, and this corroded away to nothing within 5 years. Dad's solution was to remove the rusted steel and fabricate a new top, made from some 3mm stainless steel filter mesh ( overkill, but it was free) and make a new stainless steel impeller for the fan, and the oven ran for another 2 decades of use after that. Only reason it was replaced was we moved to a smaller place, and it was too big to fit the kitchen.
Myself I have a KIC microwave, made in around 1984, and it still is running perfectly well.