I've heard of pads lasting 15 years before they need to be replaced. As long as the ones that will be left alone still seal properly, I see no reason to go to the extra expense to replace all of the pads. If the ones that are to be left alone are just in decent, should-be-okay-for-a-little-while kind of shape, you might want to get the replaced so you don't have to worry about it later. It really depends on how much you trust your tech's analysis of the situation.

Has the flute ever had a setup?

If not, your would be preping some keys and not others and that can result in a different feel and longevity of the pads. If you've had a setup, then replacing only the bad ones is fine.

6 years for pads on an flute that has not been setup can yield instability and more quickly wearing pads.

What type of flute?

Joe B

80B's usually need a good amount of setting up, these are the types of flutes that benefit in playability from a good setup.

You have to trust your tech. None of use here can really say without actually seeing the flute. However, if you want to be sure...get a repad done by a flute tech that is familiar with doing these types of setups and not just getting a "standard" repad. You'll just end up with needing another repad in another short time.

Thanks Micron for your in-depth explanation..couldn't have said it better.
Joe B