That appears to be the tube that goes through the water jacket to supply oil to the rocker arms. The kit shown above will have all the bits and pieces necessary to replace it, and it's a one time use item that cannot be removed and reinstalled without damaging it.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!