@SailingLoto I am guessing that you are near the end of your season for 2020. The mast will be down on the hard and the boat covered for winter. This is a great time to examine and explore the options to improve your halyards.
Two options are available. keep what you have or change to something different.
I had the wire/rope halyards and changed to all rope when I refit my mast. We had to address the sheave issue. The Wire/Rope sheave is not just a U shape. It has a U form but a smaller diameter groove around the center of the sheave to let the wire fit the sheave.
A cheap approach is to get a rope diameter that fits the sheave and just go for it. For 90% of the time it will work fine. As the halyard wears you may find you will want to replace it sooner than you think.
Or you can modify the sheave. The material of the sheave is often a composite material like Delrin. This can be sanded to open up the wire grove and make it a smooth U shape for rope.
Or you can avoid all this trouble and just buy replacement sheaves. The ones there are likely aged and ready for a refit. Fit the new sheave in the mast and move on to more fun.
The halyard is replaced by sewing the butt end of the new halyard to the old one and just pulling it through. Go easy. If it hangs up anywhere, just back it out, find the rough spot, clean it up or tape it and go again.
Good luck.