Power steering fluid leaking?

Twice now I have had the same problem with steering fluid leaking. Last time I was able to get it to stop by adding fluid with stop leak in it. It will leak out while sitting overnight and either have enough to make pump whine or it won't make any sound but no steering. I don't see any big amounts of fluid on the top side that would indicate the reservoir or pump to be the leaking problem. However, I do not have anything more than a jack on the dirt driveway to get underneath. So, I have yet to be able to inspect the rack and hose connections. Last time I had an oil changed they said it was leaking a fair amount of oil as it is all wet underneath. But they didn't say where it was leaking or if it was steering or engine. However, the leak started again after the oil was changed just like the last time. Oil change steering starts to leak couple days later. My question is what is the source of the leak or the main problem that will cause the leak.
I know that it can't be diagnosed without actually visually looking for the source. I just want to know what I possibly need to purchase to repair this issue. I almost ordered a steering rack and pressure line to have at the time I am able to get it up in the air and fix the problem rather than having to wait for parts and then the chance to get it up on a lift again.