"Krauss Maffei, who had also previously helped design the earlier Leopard 2" - they helped design the Leo 2? It is their very own design, even if KM is mow KMW.
Yes, Arjun had a German Engine and transmission as well as Diehl tracks, although the latter have been replaced with a licensed Indian made product.
Also, four sources on the internet usually mean one actual source, as everybody copies the other guys and if the original sources was questionable, welllll... I also love the absolute certainty of India's arch-enemy Pakistan's statement.
What I need is a statement from KM that it actually happened, but none of the people I knew there (all now pensioners, some sadly not with us anymore) has ever heard anything about this supposed design help - and they were designers.
But if the Indians are happy with the quoted versions, well then by all means the Arjun had help from Germany, it was just not enough to get it from the drawing board into service in a shorter amount of time.