83 380sl

Most of the time it starts well. Sometimes when it's hot, turn the key, get a little buzz, nothing. Turn it again, no buzz even. Can turn it 2 or three time, sometimes it will crank. Today, it did it on first start (not hot).

1. My key has a broken end-any possible way that could have any effect?
2. All the electrics check out-good battery, starter, alternator etc;
3. All times I have not been able to start, it will start with a jump off another car.

Battery, Starter, key, ingition switch? What?

Thanks.

J. Boggs