I have an '89 325i convertible with 62K miles on it. I'm having an odd problem when I attempt to start the engine. About every tenth time I try to start it, it turns over but will never actually fire off. It doesn't seem to matter whether it is hot or cold, and it can turn over FOR EVER and never start. Then you turn the key one more time and it starts right up. A friend suggested it might be the starter solenoid, which I understand is not an easy swap out. Any suggestions??