Are you talking about the tube in the top of the coupling between the front and rear rocker arm shafts? It's an overflow tube that vents excess oil from the shaft, but some of them are crimped to slow down the volume of the overflow and supply more oil to the rockers. It would be fairly simple to duplicate the overflow tube and braze it into the coupling, or simply replace the coupling with an intact one.

If you're talking about the tube that comes up from the valve lifter valley, it needs to be connected to the rocker shaft with a compression fitting to supply oil to the rockers.
Jerry

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