My 1987 300SDL has only 52k miles, bought it about two months ago. When driving down the road with either the heater on (I am from the north - we have two seasons - Christmas and winter!) or the A/C either - I hear a hissing sound from time to time. NOT all the time, not real loud.

I suspect I have a vacuum leak. Ideas? Replace all the vacuum lines since the car is 14 years old?

Can this be done by a DIY person or not?

Thanks.

it is a diyer job
 

Just take your time and take a look at all the hoses real close - even under the hood. You don't have to go to MB to purchase the hose. Just take some in and match it up. Make sure you match it up for it's service too.

I would advise purchasing a little hand pumped vacuum pump. I think they are available at Wal Mart too. You can test each device that operates using vacuum with this thing. Also, you can purchase different types of vacuum hose fittings at a well stocked auto parts place to adapt to the different connectors on your car.
Take your time and you will be fine.
Jim
'85 300D
'95 E320
'97 CRV

Thanks, Jim.

I will try it. Any idea on how much vacuum tubing to buy? I was ordering some things last week from Tom Hansen at Caliber Motors and had him send me some. Maybe 5 feet of clear and 3 feet of black rubber hose.

Thanks again.

I started by purchasing
 

3' and have already gone through it. Have about 18" of my second 3' section left.
Jim

Of the almost clear, milk jug color tubing?

the black stuff
 

purchased from the dealer. They are pretty reasonable and sell it by the foot. I have not had any problem with the milk jug color tubing but the majority of the black vacuum hose on my car was either cracked or split. All of the black vacuum hose under the dash looks good. I have even replaced some of the "X" and "Y" shaped rubber connectors too.
Jim
'85 300D
'95 E320
'97 CRV