The power steering pump in my EF has started making strange noises on start up, and occasionally the ps doesn't work until I rev it to about 2000 or so (then it kicks in).

Just after it kicks in I took the top of the reservior and the fliud was full of air bubbles (looked a bit like milk).

Anyway, thinking that before I chuck out the pump I'd pull the high pressure hose off and clean the flow value + the filter...see if that fixes it.

According to the ws manual, the O ring should be replaced if you pull of the valve/filter. I could buy the complete seal kit, but it seems a bit overkill for an O ring.

Does anyone know whether its a standard O ring or is it some special thing given its a high pressure line? ie Should I just buy the complete seal kit?

standard ones will do the trick, u will find that if u dont damage the old one taking the pump off u proberly can still use the old ones

Its not a standard rubber o-ring its a hard plastic job. Its available seperately as a spare part from Ford around $6.
I replaced mine twice and it still leaked from there so I got a rubber seal from an compressed air coupling to get a good seal, its not leaked since.

yeah Ford sell them seperately for a bloody expensive price considering them, I had to get one (mine was leaking and took it apart to find there wasn't even an o ring there). In the end I replaced the entire hose (got it cheap from work and didn't want to replace just the o rign to find later on the hose was the issue...) , stupid spare parts gofer at Ford kept trying to convince me the pump was stuffed and that if would just be the hose of o-ring, well guess what it was.