06 WQ speedo drops to zero intermittently

[pal65]

I purchased my 1.6 LX manual fiesta new in April 06. It is a great car and is driven daily (170,000km) all freeway driving.
A few months ago the speedo started to drop to zero for a short time before coming back to normal - very intermittently. About a month ago the speedo dropped and a short time later the engine cut out with the ODO showing -----. The tacho, fuel and temp gauges still worked. Once I had come to a stop, I turned the ignition off and then the car restarted immediately and drove as if nothing had happened. Once when it happened I engaged the clutch turned the ignition off and back on and released the clutch and the engine restarted, but the speedo did not, I pulled over, completely stopped shut the car down and restarted and drove away as if nothing had happened. The problem may occur once a day for 2 or 3 days and then will go away for maybe a week.
I have rung Ford and been told that they have never heard of it, bring it in and we will run some tests! That sort of response generally comes with a hefty price tag.
Is there anyone out there who may be able to shed some light on this problem?