Belt tensioner damper
 

I have removed my damper today and I was woundering if its time to relpace it?
It is the original damper. I am also woundering what is the purpose of the damper?
I have a 1988 300E M103 Auto with A/C

Put it in the vice, and try to spin the arm about the part where it bolts to the block. If it movies in a circle, it needs to be replaced. If it stays still, then its probably fine.

Since they are a bit of a pain to get out and cost so little, it's best to just replace it if it is 15 years old. The end bushings in mine were worn out causing an expensive sounding engine rattle at idle. After replacing it I couldn't believe how quiet the engine could idle!

You have the part out, change it now.

I agree
 

You're lucky if you've never had to replace it yet. Mine needed replacing after 4 years. Chances are that it will go at some point, so if it's out now you should replace it.;)

Your other question went unanswered...the damper keeps the belt in tension, yet allows for some movement due to engine vibration without allowing so much slack that the belt comes loose.

Never seen such a system on other makes, and it does appear to be an odd design, but it works.