I cannot tell you where the leak is as it is probably higher up and is running down parts etc. till it finds a low point and then drips off of there.

I can tell you how I find leaks.
Get yourself a mechanics mirror they are like a dentist's mirror just larger.
Do not get too big. The miggor should swivel. Also some of them have an extendable handle which is handy.
In a pinch I have used one of my wife's old small compacts. The type with a mirror on the inside of the lid.
Then with a flashlight you may be should to see up into the motor area etc. and with a little luck locate the leak.

Also it looks like the unit is prone to leaks and could end up warping your floor and/or in the long run rotting it out.
Get yourself a boot tray. Get one as large as will fit under the unit and one that has about a 1 inch lip around the outside. You want to cover as much area as you can under the unit.
Place this under the unit and cut out about a 1 inch gap in the front of it.
Also cut a small part of the kick plate out at this position.
Now if it leaks you will at least know it because there will be water in front of the unit.

Often it will not cover were the fill valve is so I do the same thing but just cut down a small container (tupperware etc) or make one out of double upped tin foil. Or if the spacing is OK you can just make a funnel/trough so if it does leak the water will go into the tray.

Here are your parts
Parts for Whirlpool WDF730PAYB6 / Dishwasher - AppliancePartsPros.com

If you click on a parts description a page will come up with more info on that part often with a Q&A that may help.

Yes the tray yo show will do the job as long as there is enough room width wise for it. There should be as 24 inch is a standard size.
The problem is that you have to pull the dishwasher to install it.