Those small balls are outrageously priced in my opinion! I have had the traveller blast trough the end fitting, loosing the balls in the ocean twice now. No more flimsy plastic or alu end fittings for us now, stainless steel bolts should do the trick.

You can make the 'loader' yourself if you can find a piece of identical traveller track. Just cut it so:

-------------------\
___________________\

Make the angle even more pronounced, and you can easily 'reload' your traveller car and run it over to your boats track when finished. Take care not to fill the car full, the balls need some room to circulate.
Sometimes the balls desintegrate, and you need to replace them. Sounds like you passed the critical number, and the remaining balls could not take the load. I dont think the diameter of the traveller-line have anything to do with it, the traveller car should be able to take the loads anyway.

Tieing the mainsheet to the aft-beam is a desperate move (but your only move when this happens, unless you have a spare car mounted on the track already. Like the Worrel guys did), after all, the traveller is your emergency brake when things start to go wrong so it's very nice if it's operational.

Wonder why those Torlon/Delring balls are so expensive. Are the materials so rare?