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Which rubber and plastic parts would be changed?

801 Views 6 Replies 6 Participants Last post by  jrogosich
When I finally find a 300D in the right condition and for the right price I'd like to proactively replace rubber and plastic components, filters as well as any other components likely to fail so as to start with a clean slate.

On my list thus far:
Window and door seals and runs
Sunroof seals and pads
Brake rotors and pads
Tyres
Shift bushings
Flex disks
Exhaust suspension 'doughnuts'
Air filter and elbow seals
Glow plugs
Oil filter
Voltage regulator

Could anybody help me compile a list of all the hoses, seals and other bits and bobs that would be prudent to preemptively replace in the engine compartment and elsewhere?
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In my opinion, your list is right, but replacing windows, doors and sunroof seals if the old parts are in good condition makes no sense and can actually cause problems. If you want, buy those seals, keep them and only if necessary, replace them. As said in the previous post, replacement parts today aren’t as good as the old ones and won’t last as long.

Don’t worry about replacing every possible part that may or not be worn. Before replacing, visually inspect and drive the car for a few weeks so you can determine its needs and address what really needs to be fixed.

Also, I would add to the list flexible brake hoses, fuses, injector return hoses, cigar hose, diesel filters, power steering filter and transmission fluid, filter and pan gasket.

And don’t forget to check (and replace if necessary):
-Axle boots and drive shaft bearing and carrier bearing.
-Ball joint, tie rod end and guide mounts dust shields.
-Coolant hoses and expansion tank.
-Radiator cap.
-Condition and type of the coolant.
-Engine and transmission mounts.
-Differential mount.
-And any fluid that you don’t know how old it is.
The quality of replacement parts is shit now, even the pricey stuff from the dealer.....don't replace anything unless it needs to be replaced....a 30 year old piece of rubber will outlast anything today....
The only item I can say to replace if there are either signs of wear or indications they are original are the driveshaft flex disks.

In my experience aftermarket rubber pieces are junk. I have tried them a few times and ended up doing the job twice. In my small sample size of a few MB's manufactured between 1965-2000, factory parts have always been the best route. I have purchased many rubber based hoses and parts at my local dealership and the fit and finish, at the very least, matches the parts installed at the time of production. It is not cheap to do so, but its the best path. Only a handful of times have I been let down by factory parts.

I will respectfully disagree with the notion that 30 year old rubber will be better than stuff today. In the case of hoses and such, old rubber parts decay with little visual indication. In the case of suspension joints, the decay happens so slowly, the operator tends to acclimate to wear as it happens.

All the molded rubber coolant hoses I have purchased in the mid-late 2000's for my W123 were as good as originals in terms of fit and over the last few years have proven to not have issue. The same goes for rubber suspension bushings. They certainly have gotten more expensive over the years, but in my experience the quality hasn't changed. New A/C hoses are categorically better because of the new "barrier" style plastic sleeved variety versus the old perpetually weepy rubber/braid kind.

The only way you will find out which 30+ year old rubber part has failed is on the side of the road waiting for a tow truck. If you have the means to do so, replacing critical rubber parts proactively will greatly improve overall ownership experience.
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This is correct. Trying to install a trunk seal from the dealer required a LOT of effort and the corners could not be made to fit right.
An option one of my friends uses is to patch the existing seals with rubber adhesive and parts of junkyard car original seals.
As a data point, I have had success with OE body seals from the dealership. Aside from obvious outright defects in production, all the dealer body seals I have purchased have fit as well or the originals. I replaced the rear hatch seal on my 300TD. It takes a *lot* of fussing and patience to do it right, but it fit as well as the factory one, and actually sealed. The factory one had compressed and did not seal. On both my W110 chassis and the W123, the rear window seal *looks* fine. What happens with the old rubber, even if it looks ok, it shrinks, looses its grip on the glass and both rear windows leak like a sieve.

In my college days when I barely had 2 nickels to rub together, I tried the patching route on some of my gaskets. The effect is temporary at best. Eventually the base rubber degrades and the built up silicone gasket flakes off.

The OE body moldings however, do NOT fit as good as the originals. I was NOT pleased at that.
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