To answer why stators fail, it is because the coating on the windings breaks down, usually because of heat, causing a short which can also burn the fine wire of the winding in two at the short causing an open circuit. The way to prevent failures is to prevent the heat.

What can cause a rectifier to go bad?

Things like poor grounding, a loose or weak battery, and a worn battery connection can all lead to regulator rectifier failure.

How long does a motorcycle stator last?

Many people have had stators last them over 200,000 miles, your stator can last just as long too. The main reason that stators get burned is from high amperage. If you need higher amps, it will shorten the life of your stator.