[rose_surfer]

If you do decide to remove the old silicone I suggest reading up on silicone removers available at Lowes, HD and Ace. I have no experience with them. I have sliced caulk with a stiff utility knife blade while lubricating it with WD-40.

Also, what type of silicone are you dealing with? Clear GE Sealant, White Bathtub caulk, etc.

It would be helpful to this site if you published your reviews of the products you used.

Be thankful it's not 3M 5200. Capt. George

No idea since I didn't put it on but it's definitely clear.  Didn't think about using a solvent but that's a very good idea to try to spare the o-ring.  Either way i am not going to attempt until I have sourced replacement hatches just in case.