That in my opinion is odd that both shocks would be leaking with that few miles on the car.
I have to say the thought crossed my mind that you had it in for an oil change and someone sprayed those with a little light oil and hoped to sell you something. Bad guy oil change shops use to do that.
I don't think the Steeda's would have anything to do with these going bad. The shocks are still operating within the range of the piston. Strange, very strange.
Do the old shocks still have their gas charge? If the leak is significant the gas usually bleeds off and won't rebound.
The dealer has been the only one to do oil changes so far, and the multipoint inspection from picking up the ST in May (first time after the long stint there) showed all good. And this was maybe 1500 miles later doing the first oil change on this engine.
I find it odd that both went at the same time as well, but in looking up replacement shocks I found a post on explorerforum.com where a person (also an ST) had both rear leaking as well, and they had stock springs.
I didn't check their charge, but can do that tomorrow since they are still out in the garage right now and report back how they are.