BMW Repair: expansion plugs, bmw 323is, expansion plugs

Question
My 1989 BMW 323IS overheated and I have coolant leaking in between the engine and the transmission.  My husband thinks it is a blown expansion plug.  How do you find the plugs?  Why do you think the car overheated?
Thanks for your help

Answer
It could be the expansion plug as you mentioned.To replace the plug you need to remove the transmission to determine the exact size.The  reason for the over heating is the loss of coolant.The plug probably has corroded and a hole was made.The car is 21 years old age does affect the car parts.The possibility of frequent coolant changes(every 2 years,factory recommends)unfortunately isn't commonly done as it should be done.