Sash lock help

A professional from USA says:
I am in the process of receiving keeper shims from you. This is for a home that is under contract to be sold. The buyer feels that adding the shims to make the window locks work will not allow the upper and lower sash to seal properly. The lower sash has 2 rows of felts across the top rail that meets the bottom rail of the upper sash. It appears that with the upper sash being too long, that only the bottom strip on felt will contact the bottom rail of the upper sash when the window is locked. The lower piece of felt is in about a quarter inch from each side of the sash. Is there a weather strip that can be installed that will take care of this problem without being seen and still have the window fully functioning? Or is there another way to make the seal effective? Thanks for your help in this matter.

User submitted photos of window hardware.
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Paul from SWISCO responded:
There may be a few reasons why the sashes are not meeting correctly. First, is there an interlock groove on the lower portion of the top sash that meets the bottom sash? Sometimes dirt builds up in that interlock groove, which prevents the sashes from meeting.

Also check the channel that the top sash fits into. Is there an installation screw preventing the sash from being able to go up all the way? Check the bottom sill for the same reason.

Finally, check the bottom seal of the lower sash. Is the weatherstripping twisted and preventing the sash from closing fully?

In regards to the lower row of felt that doesn't go completely over to the sash edge, we have a stick on weatherstrip, our 58-026, that might help for a while. However, constant use of the window might wear it off.
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