How do I know when my front axle seals need replace? What should it cost? on 2002 Chevrolet Tahoe

I was told by an oil change shop that I really needed this, because it would fail in a week or two. I am very suspicous of there compenence.

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1 answer 3 comments
IS THIS A 4X4 AND ARE THEY FRT OR REAR AXLE SEALS. I WOULD ALSO BE WORRIED ABOUT THEM
It is 4 x 4 and they are the left and right front axle seals
IS THE UNDER SIDE OF THE CAR COVERED IN GEAR OIL? IF YOU PULL BOTH AXLES AND REPLACE SEALS IT COSTS APPROX 400.00
Thanks for your assistance. I will crawl under tomorrow, if it is not raining, and check. Appreciate your quick response.