If the dragon is regenerating, you have brought him out to far. Keep him IN the grove. You DON'T want to diplo or inti him as you spend a lot of plat doing so, and while you get more xp, I believe you still have to fight him (not tested by me, but I remember reading this back when MoTU first came out.)
That being said, he is VERY easy to take down. I am not a power player at any means, and I can solo him with absolute ease. If you are melee, get something with ice or electric on it, if caster, stack up DOT. I also use the darkstorm helm and clickie lightning storm, that seems to bring him down a lot as well. Melee'ing him is difficult as he can run you over and keep knocking you down, and he is fast. Just keep moving, make sure to have some acid resist and protect pots, and hit from the side rather than behind (the tail knocks you over too).