Working on a 73 240Z Restoration. I just ordered an O ring and locking collar for the fuel tank sending unit. The FSM shows the sending unit going into the tank, then the o ring on top of that, then the locking collar. Is this correct? This would result to a metal to metal fit between the tank and the sending unit and offer little sealing from leakage. The one I took out had the o ring between the bottom of the sending unit and the fuel tank, then the locking collar, (which seems to make more sense). Trying to decide which is correct. Did the previous owned just install the previous one incorrectly or is the FSM correct?