I have a '74 450SEL with about 250,000

Anyway, the differential is original. I'm getting these symptoms:

1. There is a "clunk" from the rear-end when accelerating, and another "clunk" when you let off the gas.
2. The car rolls about 10 inches or so when it's stopped and put into park.
3. There is a 3-second delay between putting the car in reverse, and it actually backing up.

I'm guessing the differential is the culprit, based on the other posts I've researched ... maybe it needs a rebuild? Does this sound about right?

And if it is the differential, what is a resonable price to have the work done? ... I have average mechanical skills, but from what I've read, differential work often needs a pro.

Thanks, and cheers