This seems a serious matter to me if booster is rubbing with Air filter, bcuz air filter vibrates with your engine and this vibration will eventually break the oil reservoir bottle and can cause serious consequences (you know what will happen if bottle breaks, there will be no brakes!!!!!!).
Get it fixed immediately to avoid any disaster. i would suggest try fitting booster from some other car, may be alto japenese one etc. If no alteration found, i would suggest come back to original hydraulic brake system, bcuz safety first.