I have an 07 street glide i bought a couple of months ago it has developed a cracg in the exhaust pipe near the rear cylinder were it brakes off into the left and right has any one else had this problem ive heard that its common in this style of exhaust 

Without a pic, its hard to tell exactly where its cracked.  I'd say on the weld !!!

Is it common, i dont know, but if it is on the weld, that would be where most metal would , (if not welded properly), start to stress.

That being said,  my header pipe cracked on the weld where the active exhaust valve, (international models)  meets the header pipe, 2009 FLHT.  I have heard it happened to others, just unluckly i guess.

The good news,   it was a excuse to piss the active exhaust off , re weld a piece of stainless steel in its place, and de-cat the header pipes. Most  happy with the outcome !!!  pics below.   Cheers