I am booked in business class on an AY flight from ARN to LAX with an AA ticket. If I am not mistaken, AA still offers, unlike AY, free advance seat selection for business class (which was one of the reasons to book via AA instead of AY or BA). However, I cannot make a seat selection on aa.com (during the booking process, the seat selection sub-menu popped up, but no seat map was displayed) and on AY, in the "manage booking" menu there is also no seat selection available.

Long story short, how does seat selection work on code-share flights opb AY? If I understand the AA-small print correctly, the only way is to call Finnair. If so - any experiences if the average call center operator is reasonably in the know about the differences of what is included in business class tickets of oneworld partners?