The delrin bushes are semi hard (plastic) ones that replace the stock rubber / steel ones.

I agree, if your current bushings are in poor condition, that it will make a huge difference. When I replaced mine the difference was noticeable but not huge.

Incidentally, I am in process of currently rebuilding my rack (no options for a rebuilt RHD rack from any of our vendors) so taking a great deal of interest in this thread.

Hope you get it sorted.
Myles