But if they change it and the part is defective, it will happen again. Do new OBC perform better / did they fix them ?
I don't consider them "defective", they are just trying to make them small, light, uncooled and powerful and all that doesn't go together all that well so random failures are somewhat common. OTOH, I have more than 10K miles (16 KM) on each of my bikes with no OBC issues so far. But I also try to avoid leaving them on for countless hours at a time, by adding in external chargers even when I am not in a hurry.
They do make updates to the OBCs faily often, but I have my doubts on how much it helps with reliability. It's still the same power in the same small uncooled size.
Compare to the external Delta Q-chargers. At least for my DS and SR, The Delta-Q's are larger with better heat sinks, heavier and less powerful than the OBC, so they have a much lower failure rate.
-Don- Auburn, CA