How long do these last? Will the brushes eventually fail or bearings go bad?

In my case a single 1000 gph unit does all 3 AC units so if it were to go we have no more AC. We do let it run 24/7 all season long and the boat is now 16 years old. No clue how the previous owner used the AC though.

I am going to order an extra AC circulation pump and keep it on board just in case the original decides to give up which is usually when one needs it most. Maybe even get a spare potable water pump while I'm at it because those are rather important also. Not like you can get these at the corner store either. I did have one go out on me on a previous boat and ended up putting in an aquarium pump as a temp fix until the new one was delivered. The aquarium pump worked very well by the way.