My mixer was used for it's first 50 years in a commercial kitchen before I took it home. Yes, it was serviced every two years by Hobart, to ensure it kept running well, but it had no breakdowns while in use. After hard usage for 50 years, I retired it when I myself retired and now it is used in my home kitchen.
The only difference (I know of) between it and the new Hobart mixers is my mixer has a removable fuse on the back of the machine.
The Hobart shop did tell me, they felt my 1947 N-50 was probably a better machine than the new ones.
But that being said, the new Hobart N-50 mixers are still the best 5 quart mixers out there in my opinion. What I have observed in restaurants, hospitals, institutions, and other commercial kitchen; and what I read on internet cooking forums, support what I am saying.
Is it possible you were unfortunate enough to get your hands on a bad couple of mixers?