Doors and Windows - Vinyl Inserts for Door Threshold

I have an old Vinyl/Aluminum Door Threshold in my house. Probably from about 1958. I need to replace the Vinyl Insert. The replacement insert I purchased has an alumimum piece included to hold it in place, but my old Threshold has no piece like this or place for it to fit in. Also the vinyl piece that I bought is shaped like a C (when viewed on end) with the open part wrapped around the aluminum piece and the closed part facing the bottom of the door. The old Vinyl piece that I removed is shaped like the greek letter omega (?). Do I need to match the new insert with this old threshold, or am I more stuck in that I need to replace the whole threshold? Thank you for your help.

You should be able to find a replacement vinyl insert that has no aluminum pieces in it. Macklenburg-Duncan makes a good selection of them. Look in the weatherstripping section of any home improvement center.