I have this exact model - Echo GT 225. I was able to replace the driveshaft by simply threading it up tube. I took off the cutting head spindle, which is much quicker (just two screws) than dismantling at the engine. Be sure the tube is pushed all the way into the engine housing up to the black line. My driveshaft kept disengaging until I fixed this.
I have the edger PE 225 with the same drive shaft that had stopped spinning although the engine ran. I just took off the bottom, removes the shaft and reveresed it. I started it back up and it worked. No parts or removing a whole bunch of stuff. It took 2 mins.