I have a 1995 Silverado 6.5 TD that I was getting noise from the heater box / air distribution case when air was going through it. Turns out that the problem is there is a gate inside of the heater box at the floor where the air comes out called a mode valve operated by the mode motor/actuator which by what ever position it is in determines which vents the air comes out at, AC, Floor or defrost. The rubber seal that is on the edges of gate or valve is shot and making the noise. My question, is there a way to replace just the gate/valve without totally removing the whole heater box which looks to be a major job?