Had a quick look in bygone section.
An X3 ran in the 60's between Durham and Sunderland via Seaham.
I know this ran until the 80's.
At some point in the 80's (de-reg?) the X3 ran alongside the 220 (20/20A route).
There is a timetable from 1997, which shows the 154 doing the Sunderland - Durham via Seaham route.
I think it changed a few years after this, how long, I am not sure.
RE: Go North East Service Suggestions
'Illegitimis non carborundum'