I have a few places on my boat where the caulk is starting to show its age. I would like to recaulk these spots. I should remove all the caulk and recaulk the entire seem? Or should i just remove the spots where is cracking? Never caulked stuff on the boat before but iv done windshields and it should be close to the same concept.

Depends on what type of caulk it is. If it is 3m 5200...good luck removing it! It is a polyurethane adhesive sealant, very high tensile strength.

If it is regular silicone I would get rid of all of it and use the 3m 4200 or 5200. I used some PL brand for the rub rail on my boat, I think it was S40, also a polyurethane adhesive sealant with UV protection. It is a lot cheaper that 4200 or 5200 and comes in white, grey and black.

Mine rub rail was originally on with silicone. I bought some silicone dissolver which also comes in tubes. I have two extra tubes of it. If you are interested I would sell them cheap.

Only stuff I use in my shop is boat life- life seal.

i guess a good way i could find out is see if it pulls right off?

silicone is very stretchy and rubber band like. Polyurethane sealant is tough stuff, not quite as elastic. I have never seen silicone actually dry out and crack.