Theres alot of variables to consider regarding smoke unit failure. What exactly is the nature of the failure? I.e. 3 cab light blinks indicates a bad fan motor.
Lionel had a rash of defective fan motors a few years ago. I had a loco with one, replaced it myself and its been fine ever since.
How much fluid are you adding, and how often and what setting is the smoke unit at? The whole 8-10 drops thing is a joke, alot of folks add an entire dropper at a time.
I've found most of my smoke units smoke well enough at the lowest setting, and even so fluid needs to be added every few minutes. With the larger physical size of the resistors Lionel is now using, it doesn't take long for the fluid to be used up and the wicking to start charring.
Having said that, depending how often you run your trains with the smoke on, sooner or later the unit will need rewicking at the very least. Smoke units are not a "maintenance free" feature. The higher the setting, more frequent the use the shorter the life of the wicking.
This holds true for all brands, not just Lionel.