idle rpm

Hello,
I would like some advice for my 450sl from '75 (d-jetronic).
When the engine is running on idle, the rpm are to high (1500rpm)
I also hear a whistling sound, and when i spray start pilot near the rubbers between the both sides of the intake manifold, the rotation speed changes.
I suppose that there is a false air leak at the intake manifold rubber rings?
Is there anyone who has experience with replacing those?
Isn't it difficult to remove the bolts from the intake manifold without breaking those? (They are possibly already 45 years unbolted into the aluminum heads?) 
Any advice?
Thanks in advance!

Hello (?) Ward(?), 

No, no problems are to be expected. All parts are new available.
It is only important to use a good (new) Allen key, because they are tightened quite firmly and then become round.

Regards 
Frank

Hi Unknown,

it could also be vacuum pipes or seals under injectors. You need to further identify that leak. I recommend a fogging machine for that.