For lack of a seal, if the leak is not too bad try some Mobil 1 Synthetic ATF as P/S Fluid. I had an Audi 200 Quattro that leaked the expensive mineral oil and wasn't loooking forward to swapping the rack. I had read a few posts on an Audi board about the Mobil-1 working well and swelling seals enough to stop leaks. I figured I had nothing to loose, it worked.
I did the same flush and fill in my Jetta 1.5 years ago and it works great. I had a tiny drip, it cleared up in a week, ~$5.00 and allot less labor.
It is easy to do, and you shouldn't need more than a quart to flush and fill it.
Drain out the mineral oil and put the discharge hose in a bucket.
Turn the wheel lock to lock a few times to get old oil out.
Put the intake line in a small can of ATF.
Turn the wheel lock to lock a few times to flush the rack.
Re-assemble.
File the reservoir with ATF.