Just a thought, so don’t panic yet: Inspect the diecast trucks to make sure zinc rot isn’t the issue. If you see any swelling, warpage or what look like stress cracks, it’s symptomatic of zinc rot, a manufacturing flaw caused by an impure batch of molten zinc. Relatively uncommon, but it has found its way in Madison passenger truck castings for K-Line and Williams in the past.
I only am suggesting this because you mentioned the cars are 10 years older than the ones that are working flawlessly in your O-42 curves.
If the trucks look fine, then the problem lies elsewhere.
