Is this even possible; am I being taken to the cleaners??

I have a 1991 300CE, and the transmission went out...I took it to a transmission shop, and they said that my transmission's rear pump was broken, and that the "case" was cracked (meaning the outher shell of the actual transmission body). My bill went from $1100 for a rebuild to over $2000 for the pump and case replacement...how does the outer case become cracked? Anybody?

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1991 300CE Sportline
1983 300SD TurboDiesel (Gone but not forgotten)