The standard leak from D-jet injectors is from the swedged rubber hose at the top. This can easily be removed and the hose replaced. I would suggest doing them all as the act of removing one will usually cause others to start leaking. Get the proper hi pressure hose from a MB shop. Also get the proper 13mm hose clamps, not just any worm gear clamp. I'm in Aruba right now or I would give you part numbers.
The 1974 manifolds will work, or 77-80 ones. Use the catalyst intended for a 77on car.
Bosch Master, ASE Master, L1
33 years MB technician