I have bought bulbs from cointaker, BCspinball, and PinballCenter.eu. I have had at least a dud or few from each one of them, but every one of these sellers have been great with replacments and service.
The good news is...of all of the duds I have had, they are either bad when I first try them (DOA) or they have went bad in the first 5 minutes of use. I have never had a LED go bad after if makes it past the 5 minute mark.