Not trying to sound harsh or crass, but dude just replace it with a new one, plastic gets brittle with age and from being exposed to under hood heating up and cooling down cycles so you don't want a used. My 1999 C5 Corvette has a cracked expansion tank hose nipple and I just found a crack (a common problem on the C5) in my left side radiator coolant end tank. So just buy a new one, $80 bucks is not that bad for a BMW part LOL!