Today I re-sealed my entire intake system...thought I would share some thoughts from the expereince.
Mine is a '76 euro 450se with only 69k.
I was intent to replace all rubber parts that are part of the k-jet system, as well as the the rubber boots between the upper & lower intakes, the throttle boot, and the air filter boot. The intake gaskets got done as well, while the intake was off.
It is a fairly straightforward process....not too difficult at all...just give yourself some good time and plenty of light. If you are absent minded, take photos of your vacuum line routing and also your throttle linkage arrangment for the back together stage.
A few thoughts while/after I got done with the job:
1. I wish I had ordered the return heater hose line to change it [the one from the right side of the car that attaches to the hard pipe which then runs up to the backside of the water pump]. I was able to change out the little 2" stub hose where the hard line connects to the backside of the water pump [simple 3/4" heater hose stock here].
2. While I did perform extensive cleaning using a parts washer, throttle cleaner, and heavy duty scotchbrite on the interior plenum on both the upper & lower intakes, I wish that I had thought ahead and gotten a flex wire brush and flex hone [drill powered]. I was amazed at how much gunk was attached to the rough inner surface of the plenums. Of course, smoothing out this rough casting would make a huge increase in quality of airflow and hence power....the old 'port and polish' trick really does work! Wish I had thought of it, because it would be truly easy to do yourself without a machine shop. Also, if you are perfectionist, this is a perfect time to get your upper intake bead blasted/painted.
3. Make sure you have compressed air available to blow out any debris that may get into the intake valve area.
4. The condition of all the hoses/seals that I took off [granted, 33 years old] all seemed in great order, relatively flexible, etc. However, once I started the car up, I had to make adjustments to the on/off ratio and the idle speed, which indicates to me that I must have been experiencing some type of a minor vacuum leak
throughout the system. I suggest that you change yours out if they are older than ten years old.
5. Watch the fore/aft placement of that same hard coolant return line [the one that runs down the V against the right hand cylinder head]. If you change the little stub hose where it connects to the backside of the water pump, make sure that you still enough clearance for your throttle linkage to operate....I am speaking from experience here....if you don't check this, you will have to remove everything, remove the intake system, and realign....otherwise, the throttle will be stuck in the wide open position!
6. You should also plan to change out your injector seals and the plastic cup with o-rings that they sit in...these are super cheap and are also a source of vacuum leaks in the intake system. You will be removing the injector hold down plates anyway, so it's only a couple more minutes and less than $15 to change these, too.
7. Be sure to use blue medium loctite on all your fasteners.
8. The upper clamp on the throttle body seal tightens left hand thread.
9. You will have a chance to find all the lost bolts, nuts, and washers that have dropped over the years!
10. I had a parts washer at my disposal and still used many cans of pro quality intake system cleaner....if you don't have this when you do this job, you should have a 5 gallon bucket filler with carb cleaner and let things sit in there overnight to soften up.