Oil or ATF intermittent leak
 

My 2010 has a 103,000 miles w the 4.6 litre, 2 wheel drive , crew cab. I'm having fluid purge out of the bottom all at once periodically . Happened the first time a year ago . Mechanic kept it for a week, drove it daily and it never happened again . He replace the oil filter adapter bracketat that time. Three weelks latter it happened again . He kept it for for another week . No signs of it happening again. This time he replaced transmission filter & gasket. Oil level never drops noticeably .
The truck parks on a unlevel driveway which is exposed aggregate concrete so it's hard to identify if it's oil or ATF . Can't tell by inspecting the underneath either. The spills leave a mark on the concrete 1 foot wide by 1 - 2 ' long . Both occasions the truck was parked facing up hill.
I've been parking the truck facing downhill for the last year. Have not hard any leaks until this past week when out of the blue it happened twice again . Thinking of taking it to the dealer to diagnose but thought I would check in here first. Any thoughts would be appreciated.

Place a piece of card board under the truck, ATF is a different colour than engine oil.

Waste of $$ taking to dealer unless it misbehaves while it is there, intermittents are difficult to catch..

Thanks for the feedback. . Yea I know ATF is redish in color , but can't tell in the aggregate concrete plus being partially colorblind doesn't help. Sometimes it smells like ATF - sweet, sometime like oil. The card board is a good idea though it happens so infrequently that it would move with wind rain etc. and a pain in the ass to deal with. I have a metal pan but it hasn't hit it yet ( yes the daily parking over the same spot an adjusting the pan I have not been too good at ) Just a pain . If the dealer says they can fix the issue I'm gonna ask for a guarantee it will be solved before I go ahead . They'll probably balk and i'll then probably sell the truck as I don't want this to be on going!

As you wish, cannot help further as I dont do guesses nor miracles.

The best way to pin this down is to thoroughly clean the underneath, and run it ,but check it before it can leak and run all over.
It may only be leaking at high RPM and speed, then finish draining when parked.

Engine oil AND ATF never smell sweet so I would suspect it is anti freeze leak.
This is easy to prove, just rent a cooling system pressure tester and pressurize the cooling system, when cold and warm. Most coolant leaks leak best,lol, when cold.
Did anybody check the coolant level ,maybe they overlooked this looking for lube leaks.
I remember when given a written problem in mathematics they would throw in an entirely unrelated piece of info to throw you off. I wonder if this is not happening with an oil leak that is not there.
This could be something simple like a loose hose clamp and the pressure tester will show this.

Thank you both for your input. I'll continue to do some investigative work and see what i come up with .