To further substantiate the thesis that the puzzle vehicle is a Magirus-Deutz with Kässbohrer bodywork:
1) A picture of exactly the puzzle car, which is called Magirus Deutz (which for inexplicable reasons whether the correctness is massively doubted)
2) Another picture showing a Magirus Deutz with a very similar Kässbohrer bodywork (which for inexplicable reasons whether the correctness is again doubted)
3) Two pictures of the Magirus Deutz O3500 bus chassis, which clearly show where the tank and the tank filler neck are located. Namely just behind the front entry
..not in the back, just in front of the rear wheels, as with the only verified Kässbohrer-Borgward.
A picture of the Borgward BO 4000 chassis would be very welcome, which may finalize a discussion, which would be worthwhile much more often on 'AutoPuzzles-website', if greedily collecting points wouldn't spoil the fun.
But only on a factual level please, which I unfortunately miss sometimes