S-670D Hydraulic fill level

[k316kane]

Looking to see if anyone would know where the fill level would be on the hydraulics in the rear end. Can not seem to find a fill line or sight glass or anything... Only thing close to a fill screw like the transmission is on the right side in front of the hydro filter area... Not sure if that is what it is and don't need to mess something up... Reason I ask is the front loader bucket is slow to uncurl and wanted to make sure the hydraulic level was correct... All help would be appreciated thank you