I have a 2007 Envoy Denali with a leaking rear suspension problem that seems very common. Some nights it lowers down to the ground, some nights it doesn't move a millimeter. Some nights it takes 1 hour to lower, some nights it takes 12 hours. I have been reading about a check valve repair kit for the air compressor, does anyone know if it is available for the 2007 Envoy? Or has anyone had the same issue that could tell me how they fixed it?