raylish said:Maybe this is why later boxes had diferent seal arrangements; I am no engineer, but I do think that putting a steel-topped seal into an aluminium casting is asking for trouble, given their different expansion rates!
I don't think the expansion rates would be the thing that causes problems, the ally casing is going to expand quicker than the steel outer of the seal anyway, and even if it didn't the seal wouldn't be able to exert sufficient pressure to crack the case, but the interaction between the steel and the ally (the same as you often see on the bonnet/boot) won't be helping. I reckon most get cracked when the seals are levered out, or fitted back in, and the effort of winding from lock to lock at a standstill.