OK all you old salts. You have a rubber gasket around your portholes. They look in good condition but are still leaking slightly. You don't think they need replacing but probably will anyway. However, to hold you off for a little while longer, you were told to clean with Mineral Spirits and then apply Vaseline. After a few hours, remove the Vaseline and your gaskets will be pliable again.
Is this a Myth or is a truism? And if there is some truth to it, why? What is the Mineral Spirits and Vaseline doing to the rubber to make it do its job?
If you only need a temporary repair, why disassemble it at all....
You must have some sealer of some type available, about anything will work...
Clean the outside seam (and the surounding area) that is leaking with alcohol so whatever you use will stick....
then use tape to mask the surounding area so the tape line is within an eigth of an inch from the seam that needs sealed.... do both sides of the seam
(If it is going to be disassembled and repaired within a couple of weeks, just use the tape over the seam to hold out the water)...
But i assume you want a "permanent" temporary repair... so after you get the area masked with the seam exposed, apply the sealer to the seam......
Now you can vigorously work the sealer INTO the seam witjout getting it all over the boat....
After you get it worked in good and evened out and the excess removed, remove the tape...
You may have a very slight tape line, but if you take your finger and gently fair it out, you will never see it or the sealer.... it will look like a professional job and will last a long time.