Front cylinder oil reserve welsch plug

[aussieal72]

Hi guys well after a few headaches and some serious bleeding we found the source of the blood loss on the ol girl.
There appears to be a small plug of sorts like a welsch plug at the front of the front cylinder it appears to be only a few mm in diameter. Oil is slowly seeping out. Does anyone know the correct name for this part and how to obtain one . Thanx in advance