I recently purchased a 1979 W123 300TD wagon. The ignition key is different from the doors. I'm not sure but I would assume the ignition has been changed and not the doors. I've read that changing the door lock cylinders to match the ignition key would be fairly easy but how about the reverse? if the doors use the original key I would much rather switch the ignition tumbler so that it would match the original key. Is this doable? Is it a difficult job?

Used to be able to get a new keyed cylinder by VIN from the dealer at a reasonable price. See if they are still available.

Good luck!!!

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Don't waste your time and money. If everything is functioning properly, why bother?
General Motors used separate door lock and ignition keys for years. I was used to that, in days gone by, and actually kinda liked it.
Plus, there's the added bonus of less wear for each key due to their only having one function and used ONLY in the ignition or ONLY in the door.
I would mark one of the keys, in some manner that suits you, and call it a day.
Just my opinion and yours may very well differ. To me, it's all about economics. I'm sure the new keyed cylinder from MB is a "pretty penny", to be sure.
You don't mention the condition of the car. If it's a cream puff, original low mile beauty, by all means I might splurge to get it back to new condition. If not, meh. Who would care, besides you, and who else would even know?

I'd go the dealer route and see if you can get the new cylinder. That way if you loose the ignition key you can always get a replacement from the dealer too.

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2004 F150 4.6L -My Daily
2007 Volvo XC70 -Wife's Daily
1998 Ford F150 -Rear ended
1989 J-spec 420SEL -passed onto its new keeper
1982 BMW 733i -fixed and traded for the 420SEL
2003 Volvo V70 5 Speed -scrapped
1997 E290 Turbo Diesel Wagon -traded for above
1992 BMW 525i -traded in
1990 Silver 300TE -hated the M103
1985 Grey 380SE Diesel Conversion, 2.47 rear end, ABS -Sold, really should have kept this one
1979 Silver 300D "The Silver Slug" -Sold

With the VIN the Mercedes Dealer will make a new ignition tumbler with matching the doors key.
They will ask you to bring the car title to verify if you are the owner of the car.
In 2002 I have the same issue with my 1984 300SD and had a new tumbler from the dealer for a not bad price.
Replace the tumbler is also a easy job.

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Nyck - TX - USA

It's possible to rekey the ignition. I've done in on a 190d:


https://www.coolcatcorp.com/Mercedes/Mercedes%20Locks.html


If you have a scrap cylinder, you may be able to salvage various sizes of wafers, rather than having to machine them smooth.

Dealers no longer deal with keys or ignitions on these models. I think they quit dealing with anything older than the 91 models about five to seven years ago.

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84 300SD
85 380SE
83 528e
95 318ic

Are you 100% on that? I recall that rumour going around a couple years ago, but I seem to remember it was proven false, or it was just one dealer that didn't want to do it anymore.

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2004 F150 4.6L -My Daily
2007 Volvo XC70 -Wife's Daily
1998 Ford F150 -Rear ended
1989 J-spec 420SEL -passed onto its new keeper
1982 BMW 733i -fixed and traded for the 420SEL
2003 Volvo V70 5 Speed -scrapped
1997 E290 Turbo Diesel Wagon -traded for above
1992 BMW 525i -traded in
1990 Silver 300TE -hated the M103
1985 Grey 380SE Diesel Conversion, 2.47 rear end, ABS -Sold, really should have kept this one
1979 Silver 300D "The Silver Slug" -Sold

When I did mine and had no problem. I agree that it was in 2002.
Just to be 100% sure I would call the dealer first.
One thing is true: Mercedes Benz like to make their costumer happy and they do whatever possible to help you.

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Nyck - TX - USA

I was able to get new master keys from my local dealership for my 1976 w115 just this past October (2020). No problem at all.

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1976 240D [W115.117/616.916] (acq 11Jun76)
1990 MB 300D 2.5 Turbo [W124.128/602.962] (acq 4Sep15)
1991 SL250d (ex-300SL-24) [R129.061/OM602.962/722.6, was M104.981] (acq 25May12, converted to diesel)
1993 Jeep Cherokee [XJ] (acq 12Apr14)
1999 SLK23 AMG Sport [R170.447] (acq 12May21 **FOR SALE**)
2008 E320 CDI [W211.022/642.920] (acq 27Jan24)

-- Deceased...
1993 300D 2.5 Turbo [W124.128/602.962] (totaled by Dominos driver 28Mar12)
2007 E320 CDI [W211.022/642.920] (totaled 18Dec23)

Since you have a E320 Bluetec, have you had any issue with your DPF?
Myne 2008 E320 Bluetec is having engine light even after DPF replaced.

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Nyck - TX - USA

I have not experienced any problems with my DPF. Currently it shows as only 19% full. Was fine even after we removed and reinstalled it to change out the motor mounts. Was the replacement properly reset in the computers? Why was it replaced? I am not aware of that being a common thing.

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1976 240D [W115.117/616.916] (acq 11Jun76)
1990 MB 300D 2.5 Turbo [W124.128/602.962] (acq 4Sep15)
1991 SL250d (ex-300SL-24) [R129.061/OM602.962/722.6, was M104.981] (acq 25May12, converted to diesel)
1993 Jeep Cherokee [XJ] (acq 12Apr14)
1999 SLK23 AMG Sport [R170.447] (acq 12May21 **FOR SALE**)
2008 E320 CDI [W211.022/642.920] (acq 27Jan24)

-- Deceased...
1993 300D 2.5 Turbo [W124.128/602.962] (totaled by Dominos driver 28Mar12)
2007 E320 CDI [W211.022/642.920] (totaled 18Dec23)

Thanks for the info. Getting a new ignition cylinder and new master key from the dealer sounds relatively affordable and easy to swap out.

Oh, and for the record. I bought a new master key for my 300D sedan within the last year from the Mercedes Classic center in Irvine, so I know you can still get the keys from them if you can provide them with the VIN number. Not sure they still provide the ignition cylinder but I'm going to reach out to them and hopefully they can still help with that. Thanks!

Changing all 4 door locks is not a job I would relish. Just getting door trim off and back on again w/o breaking old bits of plastic is often a PITA and not even possible. I mean I do it if I have to but carrying two keys in place of one is not much of an imposition.

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1986 300SDL, 362K
1984 300D, 138K

Forget tinkering with the door locks.

Either go to the stealer and get a new ignition tumbler (expensive), or buy another lock cylinder and get it rekeyed with a good locksmith (much cheaper).
You’ll get a better, likely longer lasting ignition tumbler from the dealer though.

Last I checked there were only aftermarket tumblers available. I think the best I could buy was a Febi made in China.... It’s still working 3 years and many, many uses later