BMW Repair: 1995 bmw 325 overheating, overflow tanks, clutch replacement

Question
Recently bought a 95 325i with 85000 miles and noticed during a drive around town that the temp gauge went to the red zone.  Stopped and let it cool down before driving home.  Took it to my mechanic and he said the fan clutch was in need of replacing.  They ran it in the shop for 30 min and did not see the temp rise after the replacement.  During the post clutch replacement test drive, shop called to tell me the radiator blew the cap off.  Car was not overheating at the time.  Am now told I need to replace the radiator.  Is the cap blowing off a common occurance in these cars?  Should I be skeptical about their explanation that it was just a coincidense?

Answer
Radiater problems are common on these after any overheating. The plastic  used in the radiaters and overflow tanks are known for failing.
The waterpumps with the plastic impellers are also a common failure.The blades fall off and you get no water movement.