Stihl MSA 220 C leaking bar oil from vent/valve

[BCPD199]

My Stihl just started leaking bar oil when it sits. It's definitely coming from the vent/valve. I've read that it can possibly blown out with compressed air; but, from what side? I would think from the bar side; but, somewhere I read from the oil tank side. A new valve is only 7 dollars. I can't find any info on how to replace it. Any help would be greatly appreciated.

 

[DND 9000]

Remove the valve with a suitable punch from inside the oil tank. Normally they can be blown out from the inlet side, the side shown in your picture.