The best place to farm Shredder Operating Manual - Page 12 is Ashenvale, where Withered Ancient (level 26-27) drops it at 1.8%. That is the vanilla 1.12 chance, not yet confirmed in Forever. 85 sources are ranked below by drop chance.
Gold per kill: Withered Ancient is worth about 2s 35c a kill in item drops (at Auction House prices). Gold farming spots, level 20-30
Best zones:

- Akkrilus 25.6, 63.5
- Eck'alom 52.7, 70.1
- Wandering Protector 65.4, 44.0
- Ilkrud Magthrull 25.3, 60.7
- Terrowulf Packlord 49.6, 39.5
- Lady Vespia 13.6, 24.7
- Geltharis 78.0, 42.4
- Withered Ancient 60.2, 38.5
All sources, by drop chance:
Drop% is the rate recorded in Forever once a source has been looted ten times; a greyed figure is the vanilla 1.12 chance from the world data (classic data: from the patch 1.12 world data, not yet confirmed in forever). Spawns counts the source's spawn points in the world data. "Side" names which side can kill the NPC when the other finds it friendly. The lead picks the best chance among sources that are not a rare spawn and have at least three spawn points.