I have a 88 Holiday Rambler motorhome. p30, Chevy 454. 3 sets of brakes. First 2 are disc. Rear is drum. I bought a hydroboost from a big box auto parts store. But I bought the one that was for front disc, rear drum brakes. Which IS what I have, but I am being told it is wrong. That I should have bought the one for front and rear disc brakes. There is a separate tag axle booster for the drum brakes and it is supplied by brake fluid from hydroboost master cylinder. So does anyone know if this new hydroboost will work? I could just rebuild the old one, but I dont have the output rod anymore. It flew off somewhere. If I need to rebuild the old one, where can I get a new output rod?