I have been using one from 1963 Custom Imperial daily for almost two years now and I never had any serious issues with it... I just had to replace the rinse agent dispenser as the original one made a loud buzzing when the valve opened. I used one from a newer Maytag or Whirlpool dishwasher, it was an exact match.
But don't expect great loading flexibility or dishwashing performance! The spray tube dishwashers don't have any water sprays under the lower rack and that makes the loading of some items on the lower rack a bit tricky or impossible!
The 1963-64 models had an added top rinse arm, their top rack was redesigned to be slightly easier to load and it was now on rollers so it did slide out more easily. The previous ones had Bakelite tracks which were not operating as smoothly.
I also have a 1962 Deluxe model which was almost unused when I got it. It's hooked up but not used on a regular basis. Never had a leak either.
I have a 1964 Deluxe which I got from a friend and before I had it, he had to replace a few gaskets as it was leaking. I don't think the pump itself had any problems. A friend of mine (he's also a member here and I guess he'll chime in!) has a 1957 Frigidaire dishwasher and he had to fix the pump. The only Frigidaire dishwashers I had to work more on were the newer models with the Plastic-coated tubs. Rust issues, pump repairs, timer repairs... Not quite as durable as the porcelain-coated machines but they did hold more stuff in.
I also have a KDS 14 but it needs a new tub as the porcelain coating is shot so I can't compare it for cleaning ability.