Nuprime window parts

I agree that the S390-23 is close, but it will depend on the depth of the bottom shoe. Yours is either going to be 1-1/8" deep, which will make it the S390-23, or 1", which will make it the S351-23 instead. Refer to the diagram below to see what I mean.

Comparison of the S351 and S390 balance shoes.

That sounds perfectly reasonable to me. Shoe wear happens all the time.

I do agree that the 18-110 is a good match, too. As long as the dimensions match  up then you should be good to go.