If you notice that an area of the pads is dry, check to see that you have a full flow of water coming from the spider. If not, you might try sticking a thin piece of firm but flexible wire through the end. It has to be flexible enough the make the 90-degree bend. The blockage will likely be near the end anyway, so just by picking at it you might get lucky and dislodge it. I have found picture-hanging wire works very well. If it bends too much, twist two strands of it together.
If you need to replace the spider, it is easy. Remove the screw that holds it to the top of the cooler. You will need to free each leg of the spider by slightly bending the metal holder and pulling the leg out. Once each leg is free you will need to pull the hose from the offset pipe that connects to the spider. By the way, the hose connects to the pump at the bottom of the cooler.
Once you have your new spider assembled, Screw the offset pipe into the bottom and push the hose back onto the barb. Screw the top of the spider back to the top of the cooler, and then install each leg back into the flexible metal holder. Turn the water on and you should have a good free flowing stream from each leg.