I wouldn't blame the rack just yet, especially if you aren't losing any fluid.
That could be coming from somewhere above, like a leaking valve cover, or very possibly just from changing the filter. The way the filter is situated on the side of the motor, when you unscrew it oil drains down the side of the block, onto the skid plate right in that area.
Even if the rack is leaking they'll usually function properly for a good while. Personally I'd keep a close eye on the fluid level over the next month or so and see if it's dropping at all. Maybe clean it up with some degreaser so you can verify where the fluid is actually coming from.
The lower ball joints would definitely take priority over the leaking rack for me because the failure mode on those is much more serious than losing power steering.