Edit. Continuing story. Called Ryobi parts for a Piston. Yes it's the most 'popular' seller. Funny, it's also the most expensive part they sell? Whatever, that's for another post.
I live in Canada so shipping was going to double the cost. However they forwarded me to a Canadian distributor who in turn gave me my local electrical repair shop. Piston in Canada is on back order. Dang.
So I cleaned up the Piston from oil, gouged out the crack line and roughed up the area (both sides of Piston top). Mixed up some epoxy. Let it cure for 48 hours. Leveled off the top side but left it a little proud to provide strength.
I re-oiled the moving parts put the tool back together. And.. I got my 'Pop' back. Shoots like a new tool again.
Not sure how long the repair will last but for now it's cost me nothing but some time and a few mililiters of epoxy. Hope this helps anyone else to take a look at their broken tool before giving it the heave-ho.
Cheers.