LZ
The basic cause of the problem can be traced to the engine manufacturer
The basic cause of the fuel leak was, but the "basic cause of the (near) accident" was not.
How so? A fuel leak is a "planned for" emergency. Handled correctly, then a single failure e.g. leak, should not lead to loss of the aircraft (I know the aircraft was not lost, but that came down to luck of position and good flying etc.).
Think back to why Concorde was grounded. Once it became established that a single problem (tyre burst) led to loss of the aircraft, this meant the certification criteria was not met. A tyre burst is an "exepcted" (albeit undesirable) emergency, as is an Engine Failure. There needs to be redundancy to cope with these. Same with a Fuel Leak.
So the real "cause" of the drama here was something subsequent to the leak. Drills? indications? crew? There is little point in speculating. An inquiry has spent many months investigating this, and will at some stage publish. Leave it to them... The TV program made good watching for Joe Public, but leaves many questions unanswered* as to the exact series of events, drills, what fuel was where and when etc. Not surprising when the FC, airline and manufacturer did not contribute.
*e.g. Fuel leak was from RHS? X-feed was opened iaw imbalance drills... so LH Fuel Pumps supplying RH engine (were RH pumps turned off?). So why did RH Engine flameout first? Had fuel from LHS? I am not asking for answers to these now - I am sure the inquiry will do that. Just we do not know enough to praise or criticise the crew based on heresay - which is all that TV program was.