I have had to replace it as well. And all the time having to replace the small vacuum caps on the side of the throttle body. I have reinforced them with rubber electrical tape which helped them last longer. But the throttle body adapter has lasted now for about 15000 miles. Knock on wood!!! And now that I have said it, it will probably start leaking.
I have a 2008 Hammer, at 3500 miles mine seperated, they said the glue was defective. I think new ones cost $50, my warranty covered the cost. If you think you have a leak, just move the air filter up and down and the motor will die or at least loose some rpms.