What would cause a front tranny seal to blow?

OK I pulled the tranny,as I was unbolting I noticed a huge crack in the tranny housing.Also have cracks around the starter area.Upon removal a big chunk of the housing fell out.Too funny!LOL.Anyway,I,m thinking that when I had my rearend problems(tearing the spring perches off)the force of the rear tipping up,putting pressure on the driveshaft and the housing may have cracked it?Anyway spoke with my builder and he,s gonna check it all out and if it,s good the internals are being swapped into a spare 904 I have(from the donor 73 Dart I had)Hope it,s all ok?I know for sure we,ll be swapping out the bearings.Just glad to find the problem.Pics of the 904 housing.

PS Thanks All for the help and advise.
Racing the 66 Dart 032.jpg

Racing the 66 Dart 036.jpg

Racing the 66 Dart 033.jpg

Racing the 66 Dart 034.jpg

Racing the 66 Dart 035.jpg

Racing the 66 Dart 032.jpg

Racing the 66 Dart 036.jpg

Racing the 66 Dart 033.jpg

Racing the 66 Dart 034.jpg

Racing the 66 Dart 035.jpg