I always use 5200 to install those, I don't care, usually, to replace them again so it works for me. I have a deep bias against Marelon seacocks having had more of them fail than succeed on boats that I've purchased with them installed. Some folks love them.
Sharpen a stiff, broad putty knife to a fine edge, apply some debonding agent and let it sit a bit, slide the sharpened knife in all around. It works.