2011 279c what is the intention of the cap? Hydraulic fluid filler or check location?
It's for hydraulic top up. Level check is with the sight gauge on the hydraulic tank.
So fill it to what point from here? Just to the bottom of the neck?
Till it Till it is in the safe zone on the sight glass in the tank. It is much easier to fillit with the cap on the tank. Tho it still requires 2 funnels
Refer to Cmark's illustration above and use the sight glass on the hydraulic tank to check the level.