just had to replace mine in an e-140. Pretty easy process. With the floor deflated use the tool to unscrew it until you can turn it by hand, then unscrew it fully by hand. Make sure that the threaded collar which is INSIDE the floor stays put when you take the top part off. The screen is attached to to a rubber stopper and you should be able to pull the screen and stopper off by hand, try turning it to loosen. Rinse the PRV and screen in water and reassemble. I cleaned mine and put it back in the boat in about 10 minutes, pumped it back up but it still failed at about 1.5psi and kept leaking, so I ordered a new one (leaffield A-6). Note NRS doesn't have them in stock, had to order from Clavey.
Looks like a wine bottle cork would work as an emergency stopper.