A few years back Apeks did have a couple-few batches of funky valves that leaked like the blazes, especially when cranked all the way out. DUI shortly stepped up to the plate & started replacing the problematic ones installed on their suits.
Lately, within the past few years, there haven't been any "mass incidents" of Apeks exhaust leakage problems reported.
There's nothing like a good half-hour vinegar soak followed by rinse & a hefty blast of silicone spray (white milky looking food grade in a manual pump spray, not aerosol) to keep your valves clean & working the way they're supposed to.
Within the past 10 years we've started using a non-silicone spray, McNett's "UV Tech" with very good results.
Removing your valves is a LOT easier if your suit comes with "valve ports", a rubber mounting base plate, instead of being glued on with silicone bathtub caulk.
Quality of valves: SI Tech invented the adjustable exhaust valve, they've been in business the longest & overall have been the least problematic & most reliable valves. They're also the more expensive, with some of that being due to the exchange rates between a UK company vs the Scandinavian ones, who have much more robust economies & stronger currencies.
The single best exhaust valve out there is the Viking Hazmat exhaust which has an extra check valve inside. You can hold the button in all the way for an extended period of time & they still won't leak.
SI Tech makes them exclusively for Viking. They're also our #1 seller, with the vast majority being installed on DUI suits.