NA Miata power steering question

I don't drive my 90 Miata much. I towed it to the autocross last December, didn't drive it again until August 8th(short drive to scrub in the new tires), then didn't drive it until I loaded it on the trailer for our November autox, the weekend before the Challenge. 
 

After I'd loaded it on the trailer I walked back in the garage & discovered it had been leaking power steering fluid. I topped it off, ran the event, and didn't touch it. Before the autox last weekend I checked the PS fluid & it was low, so I topped it off. 
 

Just today I finally had time to put the car in the air & check it out. There's no signs of leakage underneath, all the fluid I found was fresh & from where i overfilled it last weekend. So I turned the wheel back & forth with the engine off & discovered it had spewed fluid out past the reservoir dipstick seal. 
 

Could if really be as simple as a bad O-ring? I didn't have one the correct size, so I'll have to hit up the local hydraulics shop & see if they do. 

In reply to Pete Gossett (Forum Supporter) :

I hope that's it!  I love a simple solution. I have a similar issue and it's on my winter list. I would have never thought to check up top, but I will now!  

They're known to spew some oil past that o-ring under autox or track conditions. Haven't tested a damaged one but it's definitely a good place to start.

The pump on mine has always puked fluid from the dipstick under extended hard running. Its not bad when I'm autocrossing it, but before I got kicked out of Pineview Run I had to degrease around there after every event because the top of the frame rail would have a pretty good covering. Topping my power steering fluid off is a real treat because the charge piping runs over the top of the pump and you have to saw the top of the dipstick off to make room. I've wanted to go to the K-Power Industries electric power steering system, or mount an MR-S electric power steering pump over where my washer jug is to simplify things.

In reply to Keith Tanner & NickD :

Thanks guys!!!

I tape a rag around the dipstick and reservoir.  Cause the Zoomboni does the same exact thing. 

The escort did that, so the power steering got deleted. I'm yet to modify the Prius column to go in though.