Intake manifold

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?)
Thanks in advance!

Hi,

as this is not an injection question I propose that you rather ask it in my other forum Sternzeit-107.de which is for 107 SL/C cars. There are many people who have replaced these rubber rings already. Just post qour question in sternzeit-107.de/de/forum/forum-107en