Do you need to use "sic" for every error, or just the first occurrence?

I am typing into a computer a Civil War diary. The (unknown) author's spelling errors are actually quite consistent.

Example: "Troutman told Doug and me to ride ahead and riddjup an area to make camp." Troutman was probably from Pennsylvania and meant "read-up" the camp. The author spells this as riddjup about 40 times in a 250 page diary.

Is it necessary in a transcription to use "sic." at every error, or is it sufficient to use it only at the first occurrence.

Think how you'd feel reading [sic] for the hundredth time on the same word, and edit accordingly.

And, of course, if you're doing dialect, no [sic] is needed. Huck Finn has not a single [sic]. [Sic] is there to assure the reader it's not your mistake. This one's obvious.