I should add... these 12v LED's do not need any external components to make them 12v, they actually have a miniscule constant current chip built into the LED, to make them work on 12v, so are actually no different to replacing the bulb with another bulb. They are produced by the likes of Philips in controlled batches for high-end products, and often automotive manufacturers.
The ones most people see, are cheap LED's, mass-produced by goodness only knows who, that then have some sort of "Buck" circuit, or current limiting components, again produced in some backstreet in China thrown in. In order to keep the size as small as possible, often the components are rated with no spare capacity, and often the soldering/assembly is terrible.
All the LED's I have bought from proper accountable companies have been fine for many years.
Also the colour of the LED makes a difference. Red LED's were the first ever to be produced many years ago, and then other colours were added, green pretty soon after Red, and once those two colours were made, yellow was easy. Because of the frequency of Blue, it took a long time to be produced, and even then the failure rate for many years was far higher than the success rate. In the early days, out of a batch of 10000 blue LED's, only 8 would work, and often 3 of those would fail during burn in. In the early 80's, a red LED would cost about 20p. but a blue LED, if you could get one, was £40-£50.
Once they got Blue LED's more reliable, they could make white LED's. There are two ways to make a white LED. One is to make a single LED, with the 3 prime colour (Red, Green, Blue)LEDs inside it, producing white. The problem is, these draw a lot of current.
The second way is to do a fudge, using Phosphor. By shining the Blue light, onto a Phosphor mask, which when illuminated will glow yellow (mix of Red & Yellow light) you get the output of white light. This is preferred, as it only has one LED running, effectively only using a third of the current. As you can imagine, the scope for error doing it this way is huge, and if produced without any comeback, it is easy to make ones that last a short while, and then fail.
Hope that helps a bit..