Any non-crafted Attachments drop from Ob.
Loot pool can be at maximum:
Guignol Earring
1 Attachment
1 Attachment
Ob's Arm
All 'Pulling the Strings' Attachments can drop.
All 'Targeting the Captain' Attachments can drop.
Both Coiler and Steam Jacket can drop.
I've yet to hear/see of any double-drop of one attachment.
This is good news for those PUPs still struggling with the solo ENM because now there's a flood of those coming in as byproduct of farming Coiler/Steam Jacket and prices will drop, I know Target Marker is still hovering around 70k on Kujata though, and bound to come down a bit.