We had a situation today in one of the big shules here in Melbourne where it was raining and one of the baali korah was laining and his hat was saturated with water, it was literally dripping off his hat onto the sefer. To make a long story short, It ruined about 4-5 lines including part of a shaim.
My way to fix would be to erase and rewrite the damaged area, except I have 2 problems:
1) The water soaked right through the klaf and so I could not erase it clreanly anyway.
2) I cannot erase the remainder of the shaim, therefore I would have to make a matlis anyway.
Once I make a matlis, One should not lechatchillah write a shaim on a matlis. I must admit I have done this before but only on "old" and "bedieved" sforim. This sefer, on the other hand, is only a few years old and very high quality.
Lechorah, if I want the sefer to remain mehudar, my only option is to replace the yeriya. Does anyone have any other ideas or feedback?