I don't know that there is much difference in any of the basic zeros. They all have light duty transmissions. Kept blown clean and not abused they last a long time. If you get to a better unit- you get a lot more in performance and durability. The only thing a 757 and basic Z track have in common is the color of the paint.

As tomplum noted, grass buildup is a problem. Air hose is your friend. Every few hours blow the decks clean. If a previous owners mowed with the pulleys jammed packed with leaves and grass, wears the engine. Same for your cooling system --> radiator or cooling fins. Blow everything clean.

Zeros are called hydrostatic, but its really motor oil. Mine has Mobil-1 Full Synthetic 15W-50. Supposed to be cleaned, but I have yet to change mine. Entire threads on that here.

For me, the big problem is dealing with bumps in the lawn. Most ZTRs can go pretty fast. But your really can't do that unless your lawn is rolled totally flat.