An attribution fee is NOT required for a 55/55 Lincoln. It could be submitted for Secure Plus grading for less than $100. However, there are no guarantees the coin wouldn't Genuine. The cutoff point would be what the OP originally paid for the coin vs what its value would be if it "genuined".
Definitely leave it as is. That crack is on the side, if it was on the front or back of the slab prohibiting view to the coin, then it'd be a different story.
The only reason I'm concerned about the crack is the "air tightness". The only reason i would want it graded by PCGS is if for some reason I sold it, I may get more money for it or at least more looks. As other people have posted, a lot of people buy the plastic and not the coin. I am curious how this coin could possibly come back "genuine". Do you see something I don't?
Could be, you no doubt know more about that part than I do. I'm thinking the value of the coin alone is going to make it pricey.
No it does not. Slabs are not, and never have been airtight. What sonically sealed means is this - the molecules of the plastic are heated up, melted, with sound waves. The molecules at the edges of the two slab halves are vibrated at such a high speed by the sound that they melt together and hold the two pieces together. That's all.
ahh ok. I obviously don't want anything negative happening to this coin. like corrosion or something else. I know that may sound stupid but I really don't know. I know that copper tends to be more volatile that other metals. Is there a chemist in the house??
You're never going to have a perfectly air-tite environment. The best thing to do is store your slabs in a area that has a corrosion inhibitor and silica gel. http://www.jpscorner.com/Silica_Gel_Desiccant.htm
Getting a new slab isn't going to help anything in that regard. All you need to do to protect your coin, all of your coins, is to store them properly. Do that and you will have no worries.
Good, now just make sure you check the desiccant and change it or re-charge it as needed. And make sure your safe is kept in area where the temperature does not vary much.