It's been quite a while since I posted a Digging Through Archives thing. Making up for it.
Taken from communication between Heinz Guderian, General of Arnoured troops, and Adolf Hitler dated 1943 (excerpts):
After 2000km of traveled distance the condition of Ferdinand tanks in such that 4 vehicles ignited spontaneously while marching and became completely worthless.

Repairs are extremely hard and continuous for both unit (Heavy Anti-tank Regiment 656) and army group and can't be performed at this time.

The success Ferdinand tanks have had so far, e.g. 8 Ferdinand tanks destroyed 54 enemy tanks on November 25, indicates that the unit should be brought for reinforcement to ensure its full fighting efficiency.

Central Archive of the Russian Ministry of Defence, fund 500, inventory 12462, case N93, page 115

Actually not bad performance of debut batch of Ferdi's, especially taken into account overloaded chassis.