DIY CNC router build

Bugger .....

815 sets available, but i can not buy them! Bloody hell this has long past the point of being funny.

Thank you Clive, i'll have a chat with him as soon as i can.

Those plastic broke because the balls were not in their place, they have a very strict position where they should be located inside the nut.
You are lucky they did not bind, only an angle grinder would have set them free!
They can still be used without plastic rings but the dust will get in there and soon enough mess them up, in a year or 5 depending on use and dust.
If they are open type with a small black tube held by a screw:
-remove the screw and tube,
-insert the big screw and position the nut and the screw so the screw sits in the middle of the nut
-turn the nut so the holes are up
-turn the screw and peek through the holes till the grooves are aligned with both holes
-insert balls through one hole only till they start exiting at the other side
-put the metal lid on and insert any remaining balls under the lid
-tighten the lid
-enjoy.
If they are of the closed type, to fix them:
-find some engine grease, a flat head screwdriver, and a big clean cloth or table cover
-get the balls out and clean them properly one by one
-clean the nut inside and clean the grooves properly
-wash hands and clean screwdriver
-look inside the nut, there are deep grooves inside, only 3 of those groves are full rounds and they end on both sides where the "outside ball carrier"
-on both sides there is also another short grooved part, NO BALLS SHOULD GO THERE under any circumstances, it will lock the nut to the point that only angle grinder will work, or not because the nut will have to be cut open!!!
-make sure you got enough light to see inside the nut
-take the screwdriver and fill the grooves with grease, not the whole nut, just the gooves
-dip the tip of screwdriver in grease then grab only one ball with the greased tip and place it carefully in the groove
-repeat
-when done, DO NOT try to insert it in the srew
-find something round that can easily fit inside the nut, or make a tube out of thin cardboard or several sheets of paper
-slowly insert the tube inside the nut making sure the balls stay in place
-now slowly insert the screw, let the screw push the tube as it goes in
-enjoy.

The wipers are not a particularly good solution anyway.
If you can fit spiral spring covers, that should work better and longer.
They are not cheap, but they are not horribly expensive either.