My L button has been acting up for the past few months, basically it won't respond to the press unless there's a lot of force applied, or if I blow air on the button then it will temporarily work for about 30 mins - 1 hour. A couple days ago I finally decided to open my DS up and try to fix it, I cleaned that part out with compressed air, with cotton swab to go around the actual button and the slot that it goes into, then tested it out and it worked perfect but about 4 hours later it was back to being the same. When I blow on the button, it always works for a little bit. Anyone know what could be causing it? I was thinking it might be something with the contact, but me blowing on it makes me think different.

It could just be wearing out. These things do have a finite life span, and if you play them extensively they can wear out after a while. Pokemon Blue was single-handledly responsible for wearing out the A button on my Gameboy Color.

The DS, DS lite and DSi buttons break fast and usually the L and R buttons are the first to go

I have a friend with 3 DS's (one phat two lites) and only 2 shoulder buttons work between them all. An R on one and an L on the other, and one with neither.

The shoulder buttons do go. Almost certainly the biggest fault with the handheld.

>_<  Bummer, I was hoping it'd last me perfectly until the 3DS.  Still though, I've had it for 4 years now so pretty decent I'd say...  I suppose I can get by with breathing on the button, just looks a little weird in public haha

This is going to sound odd, but I heard it from somewhere else and it worked on my GBA SP's R button.  If you suck on the affected buttons, then blow on them, they'll work again.  

" This is going to sound odd, but I heard it from somewhere else and it worked on my GBA SP's R button.  If you suck on the affected buttons, then blow on them, they'll work again.   "