Is it leaking between the hose and the nipple or between the nipple and the injector case? The nipple can come loose in the injector case which can happen if you bend the nipple such as by using an inappropriate socket. I'm not aware of any repair for this other than to replace the injector. It might be possible to transfer the case from another injector. I don't know if that disturbs the setting of the injector.

Are you using factory spec braided return hose?

Sixto
93 300SD