Did he test the alternator output as I mentioned?

Is it overcharging?

It must be tested and diagnosed to be properly repaired.

If it's overcharging, a new regulator will fix it.

*Is there engine oil on the alternator from oil leaking at the front of the engine?

If the alternator has oil leaking on it, it should be re-built or replaced and the oil leak repaired.

My 1992 300E did what you describe, alternator was putting out 15+ volts and was cooking the battery and would have damaged other electrical systems if it continued.

Please deal with it before you have more problems.

Acky