Spring cleaning (Rossel flap housing, vacuum system ect.)

Servus Omeganer, I finally have a vacation and want to get my fat guy back on track and have a few questions to the experts. Have the hoses to the throttle flap through and cleaned, the thin hose is so completely consistent. But if you connect it to the throttle valve housing no air goes through (mouth to hose breathing). Is this OK or does it have to go through air? I cleaned the riser tube, a lot of oil coal came up. I am looking for a black hole which makes my oil disappear. All about 1000km missing 1.5 l (BC warning light is reported) Does there have any idea what it can lie about? I can close it; No oil is lost (dry) No oil is burned (no blue smoke, no strange smell) No water in the oil or other Aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa t. Can it be that it was on the slicked riser tube? It was not completely dense but already pretty dirty. Thanks for the help