The Old Masters.  Of the Service Clans the Old Masters naturally age the same as their mortal race. They quickly lose weight once turned becoming gaunt, lose their hair, and are physically the weakest Vampire clan. 

The Old Masters feed on Health living their victims feeling sick and fatigued. Old Masters slowly decay becoming deathlier. All injuries fade away at the end of each day allowing them to fully reform so long as their head or heart remain intact. They can command and take the form of owls. Old Masters can amplify the natural abilities of other Clans and weaken material weaknesses for them. Old Masters can take and instill skills and knowledge from other undead and are the only Vampire species who can learn magic after being turned. The Oldest of their clan can take positions normally exclusive to the Aristocratic clans. 

Sunlight is lethal to the Old Masters. The Old Masters have no material weakness, but they can only live slightly longer than their origin species extended slightly when they feed.