Power Steering problems

[therym]

hi. I own a 99' SS Convertible. sub 50k miles. I started having problems with my power steering (pump I thought) groaning and grinding when sitting in a drive through or parking lot. Once I would get back on the road and up to speed the sound (and feel of the strain through the steering wheel) would lessen and go away. Took it to a shop and they replaced the power steering pump. First thing out of the box we noticed that it was different. There are only 2 bolt holes to attach it with compared to the 3 of the stock piece we pulled off. We confirmed with the parts store that it was the right part, put it on and it was fine for about 3 weeks. Then it started doing what it had before. Thinking maybe the brand was a bad choice I ordered an AC Delco remanufactured part for twice the price of the first. I took it to the shop and we started replacing it. The fluid that was in the system was almost a chocolate milk, foam consistency. So we flushed and replaced all the fluid. Now, 3 weeks after replacing it, it is starting to do the same grinding and moaning after being in a parking lot fora couple of minutes. When it gets warm, or whatever its doing, while I am in a parking lot or drive through, fluid starts leaking out of the top of the reservoir. If its driven and not in a parking lot this does not happen. I have replaced the cap thinking it was a bad seal letting air in but its still doing it.
I am at a complete loss as is the mechanic. Is the pump just not made for the 17" 275/40 stickies? Why does it only act up when I am in a parking lot or drive through? Anyone at all seen something similar to this? It is driving me nuts.
I read some posts on camaro28.com where people were saying the rack and pinion needed replaced for similar problems. We haven't seen a leak or any signs of play in the rack and pinion. Today I opened the power steering fluid reservoir and the fluid looks perfect. the cap spring and retainer flew off of the cap and broke the end of the dipstick off and somehow all landed in the reservoir, which I had to dig out.

[Orcus79]

Ahh, ok, what has happened is that power steering cooler (the metal pipe in the lower rad hose) has cracked. Which is why the fluid was all milky. If you pop the rad cap off I bet you that there will be an oil slick in there.

[therym]

Well, I will have to do that today and see what the coolant looks like.
Is a replacement cooler easy to find? Or are there aftermarket coolers that are better?

[Orcus79]

I have no idea. Probably a dealer specific part. I would guess though that if you searched you could fine an after market cooler pretty easily. In my books any load you can take off the cooling system the better.