How about extending one 71 an hour to Seaham (there should be enough time to add just two vehicles to the pvr with the Houghton - Seaham section do-able in 30mins each direction).
This would alternate with an hourly 266 service. Seaham - Gillas Lane - Burn Inn - Houghton - A690 - Rainton Bridge - West Rainton - East Rainton - Pittington - Sherburn Village - Sherburn Road - Gilesgate Bank - Durham.
It would need a PVR of two (if my workings are right of approx 60min journey in each direction).
To keep things right in Houghton, Seaham bound buses would need to swap over the road with the Sunderland services.
Edit - East Rainton THEN West Rainton...
RE: Service Suggestions