The Convair was sold under the "as is" condition. That leaves little room for the seller to spend a lot on test flying (fuel and other costs) and/or costly repairs.
That must have weighed heavily in the crew's decision process.
I think if you expect as a pilot to fly this plane from South Africa to the Netherlands, you would spend anything it requires to make this trip safe. If you would like to detect issues, you probably want it at your origin of the trip, not somewhere over the raiforest, desert, grasslands or war zones of Africa...
As the mechanic was expected to join the trip, I would expect him to make damn sure everything is working fine. I can not believe in enough "adventure spirit" to start the long trip without spending anything it takes to make it safe.
If the report is right, it is really hard to understand why they never bothered to address the engine fire...
the BMEP gauges are simply torquemeters.
How does this fit the current replacement/repair of one of them? For me the report sounds like they suspect some sort of leak in the MAP sensor line as contributing factor for the power loss/fire, but maybe I misunderstand that point.