just a bye the bye.
QUOTE now have same wagon hitting the Frog point and now another.
What mm. b/b, did you get?
Remove,both Troublesome Trucks,run the rest thru, testing all sidings.
Replace 1. T/T, run em all again, if T/T still plays up , turn it 180*, run again,
If ok, Replace 2 T/T, if trouble with that one, turn 180*.
Just run the 2 T/T's with the shunter, check all coupling are "sliding" correctly when they take the "curves" on the Y. and not binding...
Only a suggestion.............