well my friend i think you are going to have to buy a new radiator.if there is a crack in the plastic around the expansion tank from my experience it can not be repaired and have it last. if it was just the bleed screw you could replace that for around $2.50. also, if this the original radiator you have had a good life out of it. i replaced mine in my 93 , 2 years ago. try vinesbmw.com for a price ref. they have treated me well on parts prices than a dealer...