(24 Jan 2016, 5:25 pm)GMitchelhill wrote More than likely 6038 was receiving repairs at Chester Le Street, and was just borrowed for the replacements.
I believe the Metro Replacement services are only operated by the bigger depots such as Riverside, Deptford and Chester-le-Street, and not by small outstations like Crook, Hexham or Peterlee.
6038 has seemingly spent the weekend at Chester-le-Street, presumably just to sort out a small defect. It was scrambled yesterday morning, when 4929 couldn't operate the 08:40 Newcastle-bound X25 to time as an ambulance had to be called for an ill passenger, and another driver came from the depot to take over the situation and allowed the original driver to run light in 6038 to Newcastle, to perform the 09:25 to Langley Park from there. 4929 then went back to the depot.