Thanks to the great service of The Fast Lane/Mercedes Shop my Voltage Regulator magically appeared on our front porch this afternoon!

I did take the old unit out and replaced it with the new one. I suppose it went OK as the bolt holes lined up nicely

Question: How will I know if this does the trick (apart from the aforementioned horrid stench)?

How do I know that the old part is bad?

Judging from the old part I pulled out - the two spring-loaded contacts were quite worn compared to the new model. Also the little resistor on the part looks like a newer (better?) version.

I hope this does the trick!

Thanks again for your thoughtful responses!