Yes, welcome Lumbes,
The cap on the cam cover may be overwhelmed by the cam lobe below it throwing oil up at it. Check under the cap if there is a sheet metal piece blocking the oil being tossed at it. If not there, then get one from Bean or RDent.
The oil breather tube is a must, at least to minimize leakage of the motor gaskets since the Twink can build up crankcase pressures. The stock steel tube had a spark arrestor screen in it also to prevent a pressure wave on carb backfire. It looks like the DPO left a bit of the old tube in the grommet to connect to. Just get the appropriate tubing to connect to the inlet side of the carbs, behind the air filter. You may have to modify the filters on those ugly webers to make it work though. LOL
Jerry Rude
4005R