Simson kr51/1 Getriebe

Hello sorry about writing in english. I want to fill my gearbox with new oil. I thought this was filling plug but there is a steel rod blocking it when i unscrew the plug. Help please

[Blockierte Grafik: http://i1306.photobucket.com/albums/s562/nx6h/IMG_0889_zps77cc6718.jpg]

[Blockierte Grafik: http://i1306.photobucket.com/albums/s562/nx6h/IMG_0888_zpsf6d44eb4.jpg]

Danke
alte schmutzige Öl 250cc,
neue, saubere Öl 450cc
Betriebsanleitung schreibt 500cc fur simsonkr51/1

Thank you old oil was only 250ml, i put in 450ml of new oil through side cover but my manual says to put in 500ml.Is this OK