Variation on suggestions - how about sanding and staining just the groove itself, then applying a little clear in layers into it (like leveling cupped inserts), then sand that flat and final coat of clear?

Anybody ever try elongating the screw holes in the arch plate only *slightly* like 1/16 or less so the arch can be adjusted lower where the ball now rolls barely below the groove? I guess that would work but then you're modifying the pf... however you can still move the arch back to original if desired.