Most leisure boat rudder shaft sizes are 1 1/2'' if yours is the same then yes 1/4 PTFE will do the job nicely.
If you have to repack, then cut a length sufficient to wrap around the shaft with an angled cut so that the ends overlap but are the same level, if can follow me.
You will need 4 of these cut initially, coat them lightly in waterproof grease
You will then have to remove the rudder arm from the top of the rudder, undo the 2 nuts.
Get a piece of old wire like a gas welding rod, wire coat hanger and file one end to a sharp point.
Bend the point over to make a hook, shape the other end to make a handle..
Make sure your bilge pump is on automatic.
Slide the top fitting up over the 2 bolts.
Use the hook to remove the old packing, water will come in but that's normal, don't panic.
Now push in evenly the first ring of packing, tap down evenly with the blade end of a screwdriver so the packing is seated flat all round.
Repeat with the next ring, offset the joins to 12, 6, 3 and 9 o'clock positions.
Return the top fitting and tighten the nuts until the water flow stops, reassemble the arm.
Check it regularly and adjust until it's fully bedded in.
There should be no leaks.