Note: I'm not familiar with the construction of Palm drysuits but that doesn't keep me from opining, does it?
First, if it isn't broken, it can't be fixed. Look the gasket over good by stretching a reasonable amount and looking over the stretched gasket inch by inch. Are there any cracks or other signs of damage? Is it sticky or gooey? If so, replace it. If not, I wouldn't worry about it.
If the stitching is good and the old gasket is still firmly attached to the top, I would not remove it. Cut it close to the fabric and glue the new gasket to the old gasket, using AquaSeal by McNett. Remember, there is a hole at every stitch point. How many holes is that total? If everything is firmly attached, this is all pretty strong, but if you remove the stitching and old gasket, you now have to make sure all those tiny holes are patched.
As for the "flat" vs the "cone" method, some tops, like my Kokatat drytop, have a flat mating surface for the gasket, vs a cone shaped mating surface such as my MountainSurf drydecks have. Use the method that matches your neck gasket surface.
This also means that there are 2 basic types of gaskets. Flat vs cone shaped. Which is yours? Yes, I've put cone shaped gaskets on flat tops and flat gaskets on cone shaped tops and it works... it just doesn't look very good(though, well hidden) and it's not quite as easy a job with a non matching gasket. Ridiculous, I know, but sometimes you work with what you've got.
There are several good tutorials on line. As mentioned at the beginning, you don't necessarily want to remove the old gasket, though some of these tutorials will show you how.
Walden's Ridge has what appears to be the flat gaskets for cheap, as well as a tutorial.
http://waldensridgewhitewater.com/store/index.php?main_page=product_info&cPath=7&products_id=24
A couple other links:
http://www.kokatat.com/media/pdfs/KokatatNeckgasketWO.pdf
http://www.bckayaker.com/gasket/index.html
Gasket aside, you may also want to check the whole suit to make sure it doesn't have any leaks. Block the gaskets, fill it with air then spray it with water or maybe a weak soapy solution. A small, very thin dab of AquaSeal is good for most holes. I'd be surprised if there were not one or two small holes, as, mine almost always have them. Danged sticker bushes.
Note: The last time I replaced the gasket on my drytop, I made the mistake of treating it first. This buggered up my repair job pretty well. I ended up redoing this 3 times in 2 weeks before it stuck good enough to use. Basically, if you're going to wash and treat the suit for water resistance, do it AFTER the gasket repair.