Be careful to allow the new door gasket to relax for at least a day before doing the installation. Take it out of the box and lay it out in a circle to help get any kinks out of it.
Also, when installing the new gasket, go slowly when stretching it over the edges of the washer drum and the door edge, being extra careful to make sure you align the gasket properly on the washer. You might want to take a digital picture of the existing gasket before you remove it, so you can refer to it when reinstalling the new gasket.
Some models have a port for the water inlet on the gasket, if your's does, install the gasket over the inlet first, then move onto the rest of it. If your's doesn't have a inlet port opening in the gasket, just be sure you have the gasket orientation correct.
Replacing a door gasket/boot is one of the things that most homeowners can do themselves and save yourself having to pay for a technician.
Here's a exploded line drawing of your washer, so you can see the parts and order of installation before you dive into taking things apart.
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