I also have a 99, Mine air bag would leak,but the SLS would make it even up until it was sitting on the bump stops. Had to put new airbags on,as they can't be repaired.
If it works when you push the button, and goes right up,keep the engine running and all doors closed and have a look at the bottom of you airbag,if it looks rusty, it could have worn a tiny hole in there.Theres a steel ring holding the bag on, it rusts. The new ones don't have it. Mine would stay up sometimes for five or six hours, then just go down. sometimes five minutes.
good luck...I know the cost of the bags here in Australia where $650 each and both mine went.
Quinny
