Toyota dealers not being able to find the problem

I purchased a Fortuner a few weeks ago. Before I bought it, it went for a technical assessment with Dekra, who picked up an issue with ABS/VSC/TRC and requested Toyota to conduct further tests. Halfway Honeydew conducted a diagnostic and only found low voltage on the battery. Based on this, I then bought the vehicle assuming all is in order. The problem has persisted since I bought it, I took it in to Toyota Hyde Park and they are now quoting me around R5 000 for replacement of a valve, based on the same diagnostic.

One of these reports diagnostics is obviously wrong, as they had the same brief and are coming back with different message. Honeydew has not returned my further emails to ask for clarity; Hyde Park is sticking to their diagnostic and Toyota South Africa is saying there's nothing that they can do to assist as both dealers are sticking to their story (although one of them must be wrong).

I'm not complaining about the service I've received (it's actually been good, especially from Hyde Park), but the problem I have is that there's someone in Toyota not doing their job properly and that's now costing me a lot of money - over and above the fact that I probably have to take it to a third dealer to get another opinion because both dealers are sticking to their stories.