I have a leak in the vaccum line. It appears to come from a valve unit attached to the air intake just after the air filter. It had no gasket attached. It was running fine prior to replacing the rocker cover gasket to stop oil leaks. Car now has loss of power and chuggs. I have tested for air leaks using a piece of hose which led me to the unit with signifficant loss. How can I stop the loss of vaccum on the air intake?.