Hi Roy,
The nylon worm should last well. If they are wearing it usually means they are not aligned correctly.
Ensure the brass gear is central to the worm. If there is an amount of play equalise it between forward and reverse.
Also make sure the gears are not too tight. Slacken the motor back a tiny amount.
My demo loco has done many hours without appreciable wear on the worm once properly set up.
It may be worth slackening back the brass replacement worm you have to help with the noise.
In the old days it was suggested to place a fag paper between the gears.
I hope that helps.
Regards,
David H.