Maybe just rainwater that got caught down in the car and released when on your drive under a different angle ??
It could be diesel if it feels greasy but you would have the lovely diesel smell, is it using any fluids at all?
Could just be condensation off the air con. If you set dial to screen, or screen and feet, the air con will come on automatically (above 8 degrees ambient or something) without dash-light showing (see owners manual). When you pull into garage and turn off, residual water/ condesation will drip from engine area onto garage floor. Nothing to worry about if it's this - fooled me too (I've only had mine 4 months).
could be coolant ,whatever it is it will feel greasy any liquid will pick up oil from the block.It could be oil coming from a tear in the high pressure hose from under the alternator to the engine block , mine broke on the motorway ,at the top of an offramp my oil light came on and brake discs/pads were bathed in oil .Thats one hard hose to replace .
you could be suffering from paranoia ,have you had the undertray off and with a torch follow the leak up to source ? could be rain water .
Hi there had similar on my Freelander, turned out to be a bolt on the top of the engine which had come loose and oil was slowly making its way down to the sump. Started off with 1 drip over night them gradually became 2 or 3 drops a night. It's worth a look you need to remove the plastic housing on top of the engine. Good luck!