Replacing window pile on metal frames

I have 35-yr-old single pane windows with metal (aluminum?) frames. I'd like to replace the pile which is missing entirely, disintegrating, filthy or just not sealing well.

The existing pile measures with a 1/4" wide tab and 1/8" deep pile. (see the first three photos).

Some of the windows are slightly bowing inward (from years of wind pressure perhaps) resulting in a gap of about a 1/4" (maybe more .. it's hard to measure but you can see in the fifth photo my fabric measuring tape fits easily in the gap even with the existing pile) -- this means when the window is closed the pile is not making contact on this portion of the window. If I press on the window frame I can close up the gap. I'm wondering if I should use deeper pile on this portion of the window or if there is a better solution (or just something to live with!).

What should I be using to replace this?

One more question (fourth photo): There is a metal thing in the base of the window I removed to get the pile sample. I took a photo of it (the fourth picture). Is this part of the frame? something that fell out of the sash? something else? Just curious!

Thanks!
Eric in SF

Thanks Paul!

Is it common for people to use slightly thicker pile for worn windows? Do you think the 58-099 would work for all parts of the windows or should I only use it only on the "looser" edge and the 58-045 everywhere else?

I've attached another file including several more photos of the metal piece. I see this on at least two windows and it seems to be attached to the inside of the frame, just under where the window slides (these are windows which slide left to open). Perhaps it's related to some kind of lock that prevents the window from opening too far?

Thanks!

The part in the bottom frame is a pivot lock that keeps the window from opening more than a few inches. Sometimes these are useless if you can lift the window above it. Not a lot of security here. More of a child lock to prevent accidents.