Swapping Hotdogs

The hunt to find the first A.P.E.Bot seed
After A.P.E.Bot was corrupted by Avila in New York City, Doc is looking to bring it back online after acquiring the secure backups that have been hidden around the word.
Doc Gibbons Hello @everyone, I hope you've had a restful week - I fear the task I have for you today is an active one. I tried my best to find our secure backups for @apebot's neural network, but it seems all of them were corrupted during our incident with Avila. Thankfully, we have a failsafe to make sure we never lose our ground-breaking work on the A.P.E. Bot artificial intelligence.
For security reasons, we hid four code fragments with trusted contacts around the world that when entered together into the A.P.E. Bot system will regenerate the neural network and reactivate the complex learning functions required to run this advanced synthetic brain. As an extreme measure, even I don't know where the fragments are located so all I can do is get you started but you must take us to the finish line.
I have contacted my old friend Dr. Zaius X. Machina who is the first link in this chain, but I must confess I found his response rather cryptic. I am attaching our correspondence here in the hopes you all will be able to compare notes and figure out our next steps. I do believe both letters are important to have the full context of our conversation.
Let's pursue this with haste. I may be getting paranoid but I see specters of the Path everywhere. We must make sure this advanced intelligence does not fall into their hands.
As always, thank you for your help. For all Apekind!
-------- Doc tasks scientists to uncover what possible information could be extracted from Dr. Zaius's cryptic message.
Letter from Doc to Dr. Zaius
Response from Dr. Zaius to Doc
Dr. Zaius wrote in the very first line:
My dear doctor, I would not change a word of your letter, though I might be so conceited as to change a few letters of your words!
indicating he modified Docs original letter by changing just a few letters of words. Comparing the two letters validates this theory when Doc had written the word CHANCE in the first line and Dr. Zaius wrote CHANGE, replacing the C with a G. Careful review of both responses reveals 24 instances of this swap between letters.
Comparison of letters
Reading the changed characters from Doc's original letter yields the phrase:
while also reading the changed characters from Dr. Zaius's response yields the phrase:
Crif Dogs is a hotdog place in New York City that inside contains a phone booth that used to be the secret entrance to a speak easy.
The Phonebooth inside Crif Dogs
-------- Scientists arrived there promptly at 5 PM local time and awaited for a top hatted visitor to arrive to show them a Vulcan sign, a reference to the greeting used by Spock in Star Trek.
The Vulcan Sign
The liaison that Dr.Zaius sent arrived wearing a tophat, and after providing them with a Vulcan sign, scientists were able to secure the first piece of the A.P.E.Bot backup seed.
First piece of seed acquired
The first piece of the A.P.E.Bot backup seed was add03dd8104195 and also recieved information as to the location of the second A.P.E.Bot seed