IF it started leaking after you turned the fridge off - you have problem with defrost system.
OTHERWISE you have problem with the sealed system or compressor start device. I will cover the latter only.
First, read this recall
, check your serial number and call Whirlpool if necessary.
If your fridge is not affected by the recall and the fridge started leaking while still running:
Check the start device first. If there is clicking noise every few minutes - this is what you need to know. Unplug fridge. Remove cover on the back of fridge. On compressor (black roundish metal thingy with copper tubing coming out of it) there is a start device with wires coming to it. Remove from compressor, turn it contacts side down and shake it a few seconds in your palm. If small pieces, looking like sand fall out or you can hear those pieces loose inside the start device - replace it.
This is the part you need: 8201799
Installation instructions are enclosed
"New10" coupon takes 10% off on that site.
If your start device is ok - check the capacitor, which is either attached or wired with black wires to the start device. Check if its capacity is close to whatever is printed on it. Replace if capacity is way off, capacitor shorted or open. That part is here
. It's very unlikely that you'll need to replace it.
If both things are ok, you may have a problem with compressor or refrigerant or refrigerant lines, which you cannot legally touch without an EPA license for refrigerants handling.