The slight leak is right on top of the rear axle/transmission, I believe at the speedometer.

I have had a friend of mine who is a diesel mechanic look at the leak. He informed me that the speedo sensor needs an O ring and that would be all. I haven't had a chance to let the Ford garage fix the problem, because they said they would if I could get it in there.

Question: If this is leaking slightly, how long do I have until I need to worry about damage from a low level of fluid? And has anyone else had a similar problem?

thanks for any info.,

 

If it is leaking out the top of the housing where the VSS sensor is connected then there is no danger of running out of oil. The oil that is coming out is being thrown out by the ring gear/tone ring inside the diff. The oil level is nowhere near that high. The problem though is contamination to the oil inside the diff. There is an o-ring that slips around the sensor. I would see if Ford will service that part separately, but I doubt it. As I recall its a thicker o-ring than normal, so you may not be able to match it up at a parts store. Does yours even have one at all? If you are unsure of the age of the sensor and you need an oring anyways, you may think about buying a new sensor. They are not very expensive at Ford. I paid less than $20 for mine. Otherwise just pull yours first and match it up to something in an oring kit. There is only 1 bolt holding the thing in place.