Power Steering Acting Strange

[Recap]

My power steering feels like it is not working when I first start up the car and start moving.  It feels like there is air in the system.  Goes away after a couple of turns of the steering wheel.  Any idea what's going on here. Why would the system be getting air in it.  I don't drive the car often as it almost winter here in Ohio, so its been sitting for longer periods of time.   But it's never done this before. 

[Steve Wood]

Sounds like it is low on fluid but I am sure you checked that.  I would then guess the pressure relief valve in the pump is not working or is sticking

[nocooler]

Has the fluid ever been changed? 

[Recap]

If I have ever changed the fluid it's been long enough ago that I don't remember!  I've had the car since I believe 95.  I have replaced the pressure line and reservoir at some point, not at the same time.  I did notice a small amount of fluid at the pressure line where it connects to the steering box a while back.  I wiped it off and it never reappeared.  Guess I'll replace that o-ring and put some fresh fluid in it and see if that cures my problem.  Any idea what size/type out is?  Thanks for the input.