Integral case latch maintenance help? (late style latches)

[aklepacki]

I have Integral Cases (late style). The bottom latch, which locks the case to the side rack, has a tendency to not slide/pop completely open completely when trying to release the case. I have tried WD40, Silicone spray, and bicycle chain lube wax, and none provide lasting satisfactory results. Has anyone found a method and/or product to keep the latches lubricated so they actually slide open properly?

[Zagando]

I'd try powdered graphite for any type of lock or latch first.

Might also be a fitment problem; I have to slide one bag forward a tad in order for it to release.