Add up the error positions you describe in your post:
1st error: E (5)
2nd error: F (6)
3rd error: N (14)
4th error: E (5)
? error: U/L Transposition
5th error: S (19)
6th error: B (2)

5 + 6 + 14 + 5 + 19 + 2 = 51,

then, accounting for the “deliberately incorporated error,” add 51, from above, to 19 + 2 = 72, which is, of course, “par for the course.”

I think the solution is: “The telling ash was simple buried” Allowing for one error, as mentioned in the text, this ought to be: “The telling ash was simply buried.”

There are six errors that can be corrected with a letter and six paragraphs on the page. I found that interesting. There was also one transposition error, which has no single unique letter. Hmm, not sure what to do with that – maybe that’s a typographical error (and thus the one deliberate mistake).

In sequence, the errors, and the alphabetic position of the letter are:
1st error: E (5)
2nd error: F (6)
3rd error: N (14)
4th error: E (5)
? error: U/L Transposition
5th error: S (19)
6th error: B (2)

Selecting one word from each paragraph, whose position corresponed to the letter’s alphabetic position, I obtained “The telling ash was with you.” The first four words made me think I had the solution, but the 5th and 6th words don’t make sense.

So I reconsidered the possibility that the transposition error isn’t a deliberate, non-cipher error. I think, instead that it’s an indicator that the transposition code for the system is changed somehow.

Figuring out the shift is a challenge, because there are many possibilities, once the simple alphabet position is dropped; I decided to work backwards a bit. It seems that the only word in the sixth paragraph that is a really good candidate to finish the sentence is “buried.” Nothing in the fifth paragraph leaps out as well, but “simple” seems close to a word that popped into mind immediately after reading the first four words, “simply.”

Wishful thinking, perhaps. But I tried to see what I could work out for the position of these words. If I start counting from the second sentence of these respective paragraphs, the position is 18 for “simple” and 27 for “buried.” If you take the mod(26) operator for these, the two numnbers, 18 and 1, seem suspiciously close to the corresponding letter positions for the errors, 19 and 2, and have the correct spacing.

It is possible to arbitrarily define a shift to the transposition code after the transposition indicator, to make this fit the target text. The shift I posit is:
1. start counting words from the second sentence
2. add one to the basic alphabet cipher (or rotate the transposition so that B = 1)
3. add 26 to the cipher number up to (or through) the letter L

This provides the solution I offered. I think the change after the transposition error is a bit arbitrary, which makes it a little unsatisfying, but if you believe the code is as simple as one word per error, it’s about the only sentence that makes sense.

The text is very specific about some dimensions (e.g. “five feet in height, eight to ten feet wide” – is there a reason we need to know the exact size?), but vague in other areas (e.g. “some the size of the palm of your hand” – why not use inches?). In the last paragraph, is there any reason for using the numbers “twenty-jillion” and a “million”? He calls special attention to a “million” by adding “a myriad” immediately afterwards, which is incorrect: a myriad is 10,000, not a million.

I noticed right off that there’s a misspelling in the first sentence: “baside” for “beside”. Then in line 1 of the last paragraph, there’s “he advised” for “be advised”.

Then the odd sentence in the paragraph before that: “That, right, I have!”

“Our investigator found that site, alright, …” That last is probably an extra word with part of the cipher.

It does go to show that there’s more to this than RSA encryption.