hey mate, bout a month ago I had my car serviced at the local dealer and they told me that my rear main seals and sump have a small leak. From memory it was around $800 and to difficult to do yourself... my solution, a good ol' drip tray
Yep thats true but it should also be pointed out that often it is not just the rear main seal leaking, but also the rectangular housing plate this seal is held into. To replace the seal on this plate requires the sump to be removed also which makes it a pretty big job all up. Replacing the rear main seal only, works sometimes but others makes no difference or even worse as the machining tolerances in the plates vary and are eccentric. If the leak is only minor id go with the drip tray suggestion and a can of degreaser every 6 months or so.
Mate just a word of warning re your leak. Have a look from above the rear of your engine and just make sure it's not a rear intake manifiold seal leaking oil over the bellhousing and subsequently finding it's way down to the bottom. Mine had a fairly reasonable leak and at first glance from the underside it looked like a rear main seal gone. Did the seals and gaskets and degreased everything down and she's all good underneath now. Worth a look before you go too far.