cracked convert transmission

[newbedoo]

Going to look at a 1976 convert with 30,000 miles on it. The owner has had it for 2 years and says there is a hair line crack in the transmission housing.  He says it does not leak and works fine. Is this a common problem with the converts? Or any idea what would cause a casing crack ?
Thanks

[Antietam Classic Cycle]

Not a common problem. Causes? Bike was crashed or horribly abused? May not even be a crack, could just be "casting flash" or something similar.