General Prepwork on Suziescudo

[Suziescudo]

Well, I worked on suzie scudo releasing the rear offside brake(with help from brother) and ripping out the internal fittings which were left in the back, ready to plan the campervan. Gave her a deep clean inside so now smelling much better.
Had to put engine oil in, spotted another oil filler further back in the engine, does anyone know what this is for?

 

[Suziescudo]

 

[jackwhoo]

Possibly fuel filter.
Post a picture it will help.