Chol Hamoed Question

Firstly, a gemar chasimah tovah to everyone, and apologies for the recent lull in activity. I'm sure everyone else has been busy as well. (This is the first time I am looking at this forum in a month!)

Today I was asked to repair a slightly damaged letter ( by moisture (probably spit)). I immediately noticed a large gap on the page,  after the word "bemisporom" which I thought may even be the width of nine yudin combined (which would be possul since it is acceptable as the shiur stumah, and there is not supposed to be a stumah there).

See picture below

After closer investigation it was determined that the space is not large enough to fit 9 yudin, but one could fit three large letters there, which is the accepted shiur stumah of rabbeinu Tam. Such a space is not possul but definitely somewhat problematic, as can see here in this excerpt from the L'dovid Emes (footnote 4) , who rules that one does not stop reading from it in the middle of the kriya, but one should not take it out after that until it is repaired. See below....

(Some say even a gap of only 3 yudin is bedieved - but that is not the accepted opinion and is very machmir. Rabbi M.S. Klein Sh' rules that it is even mehudar , with a space of 3 yudin between words. Personally, in the case of tefillin and mezuzos, if I can, I try to fill the gap in a bit by extending the letters on either side, (without detracting from the shape of the letters).)

I wonder what the din is on Chol Hamoed, if repair would be permissible. I am not a posek, but if it was possul (and needed for the last days of the Chag), one would be permitted to fix it. However since this is still kosher (according to the strict letter of the law), I should think it would be alright to leave it and fix after the Chag. One could still use it in the interim.

(I would have asked a Rav, however this particular Sefer Torah belonged to a Chabad Shul and it is well known that the Shulchan Aruch Harav does not mention the whole 3 letter concern so Chabad Poskim say it is not a problem. See below in footnote 50 from the Mishnas Hasofer, Rav Shtern Sh' specifically mentions that it is a non issue according to the GRa"Z. (Apologies, I don't know how to rotate the image). So definitely not a concern here and I could not justify fixing it on Chol Hamoed.)

Wishing everyone a good moed and a good kvittel.