I am going to replace my axle shafts and have one question before starting this weekend would you guys replace the diffential seals even if they are not leaking oil?

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84 300 Turbo / 320,000
96 E300 D / 55,000

No.

Ken300D

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1982 300D at 351K miles
1984 300SD at 217K miles
1987 300D at 370K miles

I replaced the diff on the SD and the seals looked fine. I reused them.

If they have the 302K miles in your signature, I'd replace them. Seals are a wear item. At the very least, inspect them for wear at the lip. When new, the lip is essentially a point. With use, the lip develops a flat that gets wider with time. It may wear to a degree where it can't effectively keep water and contaminants out of the system.

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95 E320 Cabriolet, 159K