The Arion and Roctek pedals are notorious for failures in the potentiometers. The small cheap pots have extra-long shafts and are mounted directly onto the PCB. The long shafts provide more leverage, increasing the chances of something breaking.
It's possible to replace these pots in some cases. With the Arion Stereo Flanger there isn't quite enough room to replace all 4 pots with standard 16mm Alpha pots. But you *can* replace the two outside pots.
An example is shown below. The outside pots have been replaced with Alpha 16mm pots. The pots are now mounted on the pedal housing. The original Arion knobs wouldn't fit on the Alpha shaft. Some filing, or drilling out, is required so that the knob can go onto the new shaft. The plastic bar that goes across the pot shafts inside the pedal housing was also cut so that it only went across the two original shafts.
This pedal lost it's original battery cover. Generic replacements are available directly from Arion.