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Yep. The top one comes from the tranny, and the bottom one goes to it. The bottom one is the return line that you want.
 
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Discussion Starter · #23 ·
Thanks.

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On 722.6 transmission, by the right side of the oil pan, there is this transmission hose connection. I've seen video showing disconnecting the hose at this location to flush the ATF. Does the W220 also have this connection by the right side of the oil pan? Is there other place that we can do the flush?
 

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Discussion Starter · #24 ·
I've never separated that connector before. After the flush, to connect it back, is there a washer that needs to be replaced? Is it recommended to put some thread sealant on the thread before they're connected back?
 

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You can do the flush right at the transmission, but it's more of a pain. If you do it at the transmission, it's a banjo bolt connector that uses two copper crush washers. The positioning is also, for me, a bit more of a pain to direct the used fluid into a container because of the position of the line and the shape of it, i. e. it's not easily bendable without stress-fracturing and breaking the line. So, the connector that you photographed, the one as the return line comes out of the radiator, is the easiest place. There is no washer that needs to be replaced, nor do you need thread sealant. The factory doesn't use either. It's a compression fitting.
 
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Discussion Starter · #26 ·
Thank you very much.

I now have good idea what it involves. My 1999 E320 (204K miles) is due for a complete transmission service. I will do it on that car first. I think the S430 also have that connection at the right side of the motor oil pan.
 

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I'm sure that there is, but I generally just snug it up to about how it felt when I took it off. Good and tight, but not "Hulk Hogan" tight, is where you want it.
 
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Discussion Starter · #29 ·
Agreed. That's what I will do. I'll also use some marker to mark it's position before I take it apart. After it's done, I'll try to tighten it back to the original location.
 

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Could be; since I don't do it every day, I forget which side is the side that turns. But you're in the right spot. I do recall that the sizes are 17mm and 19mm.
 

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Discussion Starter · #35 ·
I think this is the connection goes into the radiator and an O-ring needs to be replaced once it's opened. I wonder whether it is the same kind of compression fitting on the other end that will be loosened to do the flush.

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I don't recall having to replace any O-rings when I opened up the return line fitting during my tranny flushes.
 

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Discussion Starter · #38 ·
Jacked up the S430 today, it turned out that by the right side of the motor oil pan there is no connection that can be separated. It seems that the flush has to be done at the radiator connection or at the transmission connection?

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Discussion Starter · #39 · (Edited)
One way to do it is to do it at where the ATF return line connects to the transmission.

Another way is to buy a used ATF return line from eBay and sacrifice it by cutting the metal pipe portion off, connect it to the radiator and use it to flush the ATF.

The line that pumps ATF into the ATF cooler in the radiator does have that connector that can be separated. I'd think that the ATF flush can be done at that line.
 
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