VSS Issue? Speedo intermittent

[djvivid]

Transit mk6 350 LWB Box 5 speed RWD 2.4 TD (125power)

Our Speedo only works after 10-15 miles or so. It starts to splutter into life, then and after a few more miles its perfect. Everything else on the dash works fine.
We checked/cleaned all the connections they seem clean and fine. Could this be the VSS sender unit in the gearbox itself that's freeing up after the gearbox gets up to temperature?