@Pretendo
From searching for a solution online, I can confirm that this is a very common problem. I seem to have been somewhat unlucky in general with my DS Lite, though: only a month after buying it, with only normal usage, I already had about 5 pixels die on the top screen, so I had to ship it back for repair (which was free, fortunately). Just after the warranty expired, however, I've had the shoulder button issues, mostly on L but also sometimes on R. Also, there is a very slight gap where the lower screen joins the body ever since it returned from that initial repair, but not really noticeable unless you are looking for it.
For the record, however, this is the only piece of Nintendo hardware I've ever owned that has malfunctioned, and, having been a fan since the earliest days of the original NES, I've given my share of Nintendo products a good workout.







