So 8 free-spinning axles, 8 with wipers. If you flick the free-spinning axles do they all spin down after roughly the same # of revs? In other words, can those be ruled out as an issue?
If you manually launch individual cars down the track, do they all roll the same distance?
Hard to imagine how all 4 cars would simultaneously go south in 2016. Since you've been running this set for many years did you happen to store the set differently than other years?
Perhaps while waiting for weaker springs perhaps run with only 1 wiper-ed axle per car and possibly some flicker but at least keep the train in service for this season.
