Thermal paste needs a clean surface to spread properly.
You can't remount without cleaning out the old paste first.
Most likely, your mount of the stock intel cooler was not good.
Look at the back of the motherboard to see if all 4 pushpins are completely through the motherboard and locked.
If they are not, you need to remount the cooler.
Clean off the old paste with alcohol.
Use lint free paper like a coffee filter.
Place the cooler so that all 4 pins are oriented over the holes in the motherboard.
Push down on the entire cooler so that all 4 pins are through the motherboard.
When you push down on the top black pins, it expands the white plastic pins to fix the cooler in place.
The trick to getting it on is to push down on a diagonal pair of pins at the same time. Then the other pair.
If you do them one at a time, you will not get the cooler on straight.
AS5 is fine, most others are about as good.
Go to their web page for a pictorial tutorial on how to do it.
The key is to not use too much. Too much will act as an insulator; only a drop in the center is really needed.
With a "K" cpu, you will want to do at least a conservative OC.
I suggest you invest in a $30 tower type cooler with a slow turning 120mm fan such as the cm hyper212.
The backplate mount will be easier, and the large slow fan will keep your cpu cooler and quieter.