Could be just water from either light rain or condensation on the car, stick your finger in it and see if it's oily first guess if it is would be brake fluid then engine oil, the sumps are known to last only about 5/6 years, duck down at the front and have a glance if it looks bad it could be that, you would see clear evidence of oil on the rusty sump.
If you park in the same spot and it disappears over a day or so it's probably water not any type of oil, a easy check.