crank seal oil leak

Sounds like the crank shaft pully has a groove in it from the oil seal rubbing on the machined surface. When the oil seal is changed it just rubs on the same spot hence the  leaking. You need to install what is called a bearing buddy, basically what this is, is a thin stainless sleave that is a tight fit over the old machined surface and provides a new clean (groove free) contact surface for the oil seal to seal against. They work very well, also when installing the crank shaft pully through the new oil seal use gear oil to lube both the oil seal and crank shaft pully rather than engine oil, it works way better in first start up situations. 
 
Scott