About a month ago, a sofer corrected a mistake in one of our shul's Torah scrolls.
I found the mistake while reading the end of parshat Masei. There was an incorrect letter that changed the meaning of the word. The letter should have been a taf but was actually written as a heh. To make the correction, a sofer just needs to draw a line between the top of the heh and the bottom and it becomes a taf.
When the sofer came, he corrected it using a marker. (Yes, it had sta"m ink.) I didn't have time to ask the sofer about the halachot of using a marker. I understoof that Torah scrolls need to be written using a quill / reed.
Is the halacha more lenient when making a correction in that one may use a marker for corrections? Are there certain types of corrections that allow using a marker? For example, can it be used only when correcting a wrong letter such as I described above, or can one use a marker even if he has to erase a letter and write a new one? What if he has to add a missing letter?