Whoever told you that is a LIER!!! (Gasp!)
You CAN do both quests, every warlock can do (and totally should) all the quests for all their minions (with the exception of doom guard, wich actually very few warlocks take because, unless it gets buffed, its a waste of time and a pathetic pet, well, IMHO at least).
As of where the manuscript is yes there are tons of sites where you can search it, with a few names said here, but I'm sure theres a lot more.
P.S. I have thott into my firefox bar so its way faster AND I can keep alla open while I search in another window :D