Angenieux 5.9 Standard Mount & Arri SR2 – Too close to mirror?

[Valentin Meneveau]

Hey everyone,

I recently bought an Angenieux 5.9 f1.8 to be used on an Arri SR2 N16.
It seems like the lens is just about too long and touches the mirror - not allowing the standard mount to 'click in' and lock the lens.

Another thread on the forum addressed a similar issue with a PL mount, and more interestingly, highlighted a custom adjustment made to the lens's rear element:

It seems that this element has been custom filed to allow extra space to fit between the mirror and internal elements of the camera.

The lens I have received has the same element without the filed adjustment:

Alternatively, I have noticed another version of the same lens with a different rear element, probably taking in account the need for extra space for both mirrors and internal components in the camera mount:

 

My questions are: 

- Shall I return the lens I bought in the hope to get one with the right rear element? 
- Shall I try to dismount the final metal ring and file it as seen in the first example
- Can the last rear element be bought separately and swapped, fitting it myself.

Thank for any insight and help,  I'm pondering whether sending the lens back or not.

Thanks,

Val