Police have fresh leads into the bashing death of a young nanny found unconscious on the side of a road in northern NSW more than two decades ago.

Penny Hill, 20, was working for former rock band drummer Col Baigent and his then wife, Barbara Baigent, at the Black Stump Motel in Coolah when she was discovered lying on the side of the road on July 8, 1991.

She never regained consciousness and died two weeks later in hospital.

A second inquest in July 2012 failed to shed light on her attacker's identity, nearly 21 years after her death.

Police now have new information that a car seen at the motel on the night Ms Hill was assaulted could have been a Datsun Stanza, rather than a Commodore as previously reported.

Investigators will on Tuesday examine a dark blue Stanza similar to the vehicle described, with further examinations expected to be conducted over the next few weeks.

They have also collected DNA samples from a number of men to test against DNA found in the motel room that Ms Hill last occupied.

Unsolved Homicide Investigator Detective Sergeant Darcy has appealed for anyone with more information to come forward.

"Investigators wish to speak with any person in Coolah who may have seen a dark blue Datsun Stanza in Coolah on the weekend Penny was assaulted," he said.