As I understand it won't show up in a UOA. However, iirc it's needed to insure cleanliness, additive solubility and seal compatibility especially with regards to Gr3+ which behave more like PAO. I would be surprised if any modern euro approval could be met w/out either AN or ester in the mix.I wouldn't necessarily, but where's the proof of AN content? Lack of ester is not proof of AN presence per se.