Hello, I have recently had a W123 280 CE 177PS 1979 which switches hard when driving comfortably. My mechanic does not measure a vacuum on the hose at the modulating pressure box on the gearbox. The hose is directly connected to an intake tube??? in the engine compartment. So no pressure box. Maybe one of the previous owners has plugged something there? or fits that anyway. Gear oil is new inside. Unfortunately, I can’t find an explosion drawing for this line. n. Although my mechanic works on Mercedes, he has too little experience with the old ones. LG Herbert