Juhuuuuu, he's diesel again!!!!!
We almost stopped believing that this drama would end at some point....but...now it finally worked out.
For the technically interested among you:
The reason why it ripped the new starter motor too was clearly a mistake by the mechanics.
They had the timing of the engine totally wrong, so there must have been a backfire which caused the engine to start backwards.
After I was able to find a workshop manual, I forced the guys to follow this guide step by step and lo and behold...the diesel started straight away.
However, I found it surprising that the engine did not reach operating temperature.
"Hey boss, no problem boss, no thermostat inside, we lost it. But it is working. No problem!!"
After that, the mechanics wanted to increase their bill by 50%, which made me forget my manners and I had a moderate fit of rage, which must have frightened the boys quite a bit.
Of course I didn't pay the 50%!
Another comment on the brass ring gear of the starter:
We were able to have it manufactured on site, albeit with "difficulties typical of the country" ;o)
Since the ring gear of the old, same starter was still removed, we brought it to the workshop to be copied. As a result, instead of 40 teeth like the original, the Fiji copy had 50 teeth!
The replica now has exactly 40 teeth like starter no. 1 (there you go!), however, the new starter (same make, same item number) strangely only had 39 teeth and a smaller inner diameter. (HGGGGGRRRRRR... HEADBOARD BOARD STRIKE!)
Now it fits perfectly. So what!
Now all I have to do here in Fiji is find a thermostat and our adventure can continue.
At this point, many thanks, dear friends, for all the tips and advice from Germany, some really helped, but all were a real consolation ;o)
Many thanks also at this point to the company Kohl24.de from Baden Württemberg, that was really competent help!