As above, you need to get some cans of degreaser and clean down any oily gluggy areas where it could be leaking, then hose it off. Have a look in a few days and see where the oil is coming from. If its coming out of the bottom of the bellhousing and its engine oil, then it will probably be the rear main seal. IMO not worth touching till its really running out, cause it costs a pretty penny to replace that one cause it will be an engine out job. I just got a galvinised tray in my shed with some sand in it. Does the job and i dont worry about it.