Man, people should really read a bit more before making inaccurate statements.
The B-29s engines had a magnesium crankcase, when the faulty engines overheated caught fire the magnesium would eventually do so too leading to the collapse of the entire wing!
On the other hand, the leakage problems were eradicated on the A-5 and fires became non-existent once ground and air crews were adequately trained. Not to mention that the wing was significantly strengthened which allowed them to confidently undertake shallow dives, something than even the A3s were already doing in January 1944.
In the end the type had a 90% availability rate in some Gruppe, an improvement even from the 80% rate of II/KG40 in early 1944 which operated even A3s with considerable less problems than other Gruppe. As I said before, the machine was green and so were the personnel and logistics as well, and all those factors together made the debut of the He-177 a troublesome one, but those defects were overcome within a year and the machine was certainly far more reliable than some people wish to believe.
You can find the references on Griehl, pp 131 and 151.
JAG