I replaced the original radiator on the car due to the famous neck crack. After a cople of weeks my tranmission was shifting hard so I check the dip stick. To my surprise the transmission oil was pink. I thought that I was geeting some coolant in the oil due to a defective new radiator. I talked with the dealership where I bought the parts and they obliged to offer a test free. A paper test to check for coolant in the transmission fluid. The test came negative. After this I flushed the transmission oil and put in fresh. Last weekend checked the oil and it was pink. Ishowed this to the dealer and he was stumped. They did a check again for coolant and it came negative and confirm now that it is water.

Question is from where can water be getting in the tranmission. Car is 300sel.

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89, 300SEL
98, E430 black on black

There is a copper pipe the runs through the bottom of the radiator, this is your trans cooler. If said pipe cracks or leaks the coolant will mix with the ATF, it should look like a milk shake when you pull the dipstick.

Chances of the trans needing a rebuild are very high.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

eh...maybe rebuild, they can be flushed and used for many miles- I've had quite a few contaminated transmissions and have saved all but one of them. It all depends on how much contamination and how long its been happening.

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1980 500SE/AMG Euro
1981 500SEL Euro
1982 380SEL
1983 300TD
1983 500SEC/AMG Euro
1984 500SEC
1984 300TD Euro
1986 190E 2.3-16
1986 190E 2.3
1987 300D
1997 C36 AMG
2003 C320T 4matic

past: 1969 280SE 4.5 | 1978 240D | 1978 300D | 1981 300SD | 1981 300SD | 1982 300CD | 1983 300CD | 1983 300SD | 1983 380SEC | 1984 300D | 1984 300D | 1984 300TD | 1984 500SEL | 1984 300SD | 1985 300D | 1986 300E | 1986 560SEL | 1986 560SEL/Carat | 1987 560SEC | 1991 300D 2.5 | 2006 R350

Dealer has a paper test in which the paper changes colours if the oil is mixed with coolant. The test is negative and the dealer says that it is water. I thought that the transmission was pretty much sealed. Where is the place where there is possibility of water getting into the transmission.

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89, 300SEL
98, E430 black on black

maybe check if the vent cap is missing, other than that... ????

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1980 500SE/AMG Euro
1981 500SEL Euro
1982 380SEL
1983 300TD
1983 500SEC/AMG Euro
1984 500SEC
1984 300TD Euro
1986 190E 2.3-16
1986 190E 2.3
1987 300D
1997 C36 AMG
2003 C320T 4matic

past: 1969 280SE 4.5 | 1978 240D | 1978 300D | 1981 300SD | 1981 300SD | 1982 300CD | 1983 300CD | 1983 300SD | 1983 380SEC | 1984 300D | 1984 300D | 1984 300TD | 1984 500SEL | 1984 300SD | 1985 300D | 1986 300E | 1986 560SEL | 1986 560SEL/Carat | 1987 560SEC | 1991 300D 2.5 | 2006 R350

Tell me more about the vent cap and where on the transmission is it located.

Thanks

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89, 300SEL
98, E430 black on black

Is the car recently from New Orleans? you wrote that you just bought it, could be water level reached the breather port?
Just a tought.

near the top of the transmission toward the rear of it. You'll have to be under the car and possibly use a mirror to see it.

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1980 500SE/AMG Euro
1981 500SEL Euro
1982 380SEL
1983 300TD
1983 500SEC/AMG Euro
1984 500SEC
1984 300TD Euro
1986 190E 2.3-16
1986 190E 2.3
1987 300D
1997 C36 AMG
2003 C320T 4matic

past: 1969 280SE 4.5 | 1978 240D | 1978 300D | 1981 300SD | 1981 300SD | 1982 300CD | 1983 300CD | 1983 300SD | 1983 380SEC | 1984 300D | 1984 300D | 1984 300TD | 1984 500SEL | 1984 300SD | 1985 300D | 1986 300E | 1986 560SEL | 1986 560SEL/Carat | 1987 560SEC | 1991 300D 2.5 | 2006 R350