RCCadet,
Please do not feel that you NEED to change to the Nylon ones, if you are not noticing that your bearings are spinning in the Alum ones you are perfectly fine. There is no improvement in performance by using the Nylon ones, it is only to make for sure that the bearing will not spin inside. If your bearing is spinning you will be able to see the marks inside very easily.
I will be at the shop in 2 hours. It is now 12am EST, and I will get there at 2pm EST. You can call me for the tracking number at your conveniance.