I was hesitating to glue (with heat gun) my new seal as well. My old neck seal leaked… so I had to do it.. I had the one with glue strip on is as well. Did my anckle and wrist seal all ready.
Also looked here for tips and tricks but that did not really work, I just could not find something that would nicely fit in the the neck (the outside collar of the suite is smaller then the place were I have to glue..)
So then I just did it.. i cut out the old one 2,5 cm (1 inch) of the seam.. no way back.. and then it all becomes clear.
Put the new seal in (from inside suit to outside) it just fits there.. then heat one point just a little so it sticks, then work your way around so it fits nicely and when all looks nice heat good and pressure and then the next few cm’s (use working gloves so you won’t burn your fingers.. )—do not overheat!!—
Be sure you use alcohol to decrease, after that I used a little aceton as well. Do not touch the cleaned part with your fingers, it might get greasy again.
Good luck !