Leak around sliding glass door - help!

I have a home built in 1996, it's your typical SoCal stucco box. When it rains heavily, which is admittedly a rare occurrence, I get wet drywall around the sliding glass door (vinyl coated aluminum frame). There is a water stain on the paint about 1" high above the door (at the top), and some larger stains down the drywall on the sides of the door that taper out toward the bottom. Clearly, water is getting behind the waterproof paper, settling on top of the door frame, and then leaching into the drywall.
I've talked with the builder and had them out several times to locate the source of the leak, but we can't seem to find the source of the problem. Generally, this happens in particularly heavy rain with alot of wind. We spent several hours a few days ago spraying a hose at the stucco all around the door, but we couldn't seem to duplicate the problem. We originally thought that the flashing around the door was done incorrectly, however that appears not to be the case after our water test.
Our test included spraying water directly around the door as well as on several potential problem areas (speaker wire hole, electrical outlet, exterior light) and we can't seem to get any water leaks/stains like I see during a heavy, windy rain. Our only thought is that water might be going horizontally through the air vent up near the roof. Or, it's possible that the waterproof paper wasn't installed correctly and we just didn't hit the right spot with the hose.
Last night, it rained heavily *without* wind and the wall is bone dry today, as opposed to last week's rain where it was wet and mushy to the touch. I'm totally stumped.
Anyone have any thoughts on what the problem might be? Or, any suggestions on what else to look for besides ripping all of the stucco and drywall out. Is there some kind of detection device available that I could use to find the origin of the leak?
Any help would be fantastic.
Howard
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Hosing the window area does not simulate wind driven rain very well, so conclusion that door was installed correctly may be wrong. Suspect that the waterproof paper or sheathing was installed incorrectly or was cut, slit, or does not completely cover the outside rim of the door frame, but in truth, windward flat stucco walls almost always leak, tho usually less than yours, in a driving rain. Sound like water is pooling in top door channel, and porous sheetrock is wicking it up almost fast as it accumulates, but excess dribbles down sides of frame, and thru wall. Builder will often deny responsibility, that is a rule, and leaks will be "difficult to analyze". You may have to chip off stucco for several inches around top and sides of door, and see what gives. Then insert high quality flexible counter flashing that slips under mineral felt and curves over the drip edge of the door. The other possibility is, once you have the stucco removed, insert a small copper "awning" that is stuffed under the felt edge, and covers the door face for maybe 3 or 4 inches out, then re-stucco. The awning should extend a ways beyond each edge of the door, perhaps 6 inches. I'll wager your leaky door faces south or southwest! That is the real test in CA.

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I have a similar problem and don't really see a solution. Sliding doors are inherently leaky from horizontal driven water or air, although they are more or less resistant to dropping rain.
Driven rain sheets along the window, and builds up as a puddle at the bottom. If wind won't let this pond run off, it can build up to submerge channels in lower part of the door. Either the rail can be flooded (which has to have free clearance for rollers alowing water pass thru), or you may have weepage holes (maybe with flaps that possibly aren't functioning) meant to let water from the rail drain, but actually reversed in wind pressure.
There are various tweaks you can do yourself to reduce penetration gaps with screwdriver and caulk. Maybe you can improve drainage to reduce the wind driven ponding and maybe you can plant a shrub to slow down the wind.
It's very interesting to observe the door when wind/rain is coming; pretty amazing how a wall of water pushed horizontally can exploit gaps leading to channels leading to exit gaps. You may have more patience than a contractor to diagnose the real problem.
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