oil leaking fron crank case

[eranby]

Hi

I'm a new owner of 1999 GZ250 which been totally rebuild.
bike is in exalent conidition but I'm facing an annoying problem of oil
leaking...
the leak is from the of the crank case ,bellow the carb and in the point
were 2 halves of the crank case meet (there is no gusket between these
2 parts), I've tried to fix it with JB weld cement ,but the leak happend
again -200 km after repair..
I wonder if anyone familiar with that kind of a problem,and I'll be happy
if there is known solution for that.

thank you in advance and sorry for my non native English ..
Eran