We all know that our 124's are getting on in years. Some of us drive in areas where the roads are salted, etc. I have not seen anyone posting about this particular spot. I'm talking about the wheel well for the rear tires. There are a series of plastic plugs put into the metal, and then coated with undercoating material at the factory.

There is one plug on the forward side of the wheel well, above where the rocker molding terminates at the rear (and where all kinds of stones and debris collect), roughly 10" above that point. I know older cars have different rocker moldings, that's not the point...

On my '95, I had a huge water leak into the driver's front footwell which it took me forever to find, it turned out to be that plug (rear wheel, driver's side) had rusted out. I fixed it and went on, but yesterday I found the same problem only worse on the passenger side. Was poking around and pushed on that plug and pop, it fell right into the interior structure. And with a bit more poking I had a hole about 3" x 4" or so! In hindsight I could see that the undercoating was bubbled from rust underneath.

So I've patched it with a "cold" patch, just a big plate I glued and undercoated, as I don't have a welder and I'm cheap. But have a look in the rear wheel wells of your 124 and you might not like what you find...

Rgds,
Chris W.
'95 E300D, 397K

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Objects in closer are mirror than they appear.

Yes - that area is very suspect to rusting along with the entire periphery of the wheel well. The 210 is worse for this.

Those rubber plugs are actually plugs for access holes to spray wax coating on the insides of the body.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

I fixed the exact same areas in my 91 300D turbo back in 2006. Interestingly I recall the patch panels that I welded into both sides were about 3X4 inches across. Seems like 15-18 years is the life expectancy.

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98 Dodge-Cummins pickup (123k)
13 GLK250 (135k)
06 E320CDI (323K)
16 C300 (62K)
82 300GD Gelaendewagen (54K)

Same problem on my 92 300D. Like you, I had water leak that took me a while to find....even replaced windshield at indie's suggestion. And like you, I'm cheap, but even worse: I used a ghetto combo of POR-15 and duct tape! I'll have to "upgrade" to the glued plate and undercoating....

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14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 154k miles
06 E320 CDI "Rutherford", Black on Tan, 172k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 142k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife