Here's a thought: why were they at 20k' in the holding pattern? I'm sure ATC or CVR will answer this, but the MSA around there is ~13,000'. I've never flown in S. America, but would it be standard to bring them in that high and have them descend in the hold? Especially if they knew they had a fuel situation, they should have been brought in lower to intercept the ILS. Are they far enough away from major ATC (radar area) that they would have been cleared to descend in the hold and then shoot the approach? Or would they have kept them that high to let them troubleshoot prior to shooting the approach? If they were troubleshooting in a hold at 20,000', they would have known they had a major issue prior to being assigned a hold at that altitude.