Welcome to the forum!!
Is it seeping around the top seal where the metal is pressed around the plastic on top? Thats a really common place for the stock radiator to leak. I had that issue about a year ago and ran a bead of high temp gasket maker around the top of mine and have not had an issue since.
The benefit of the aluminum radiator is not necessarily in cooling, but in weight reduction. Personally when mine goes the way of the dodo I am going to find one of the XJ brass sided beasts. They actually cool better and are more durable. (if your not worried about the extra weight up front)
A lot of the aftermarket aluminum radiators come with an electric fan to replace the engine driven one, which IS really nice.