Agreed. Load may make a difference in the output. Not that familiar with the S5... wouldn't it generate a CEL if it wasn't working properly?
MAZDA's prices on these are crazy. AFAIK
, they are not designed to be rebuilt. At least that was my conclusion after examining the one from my 3rd gen. And I've never seen a rebuild kit. Good news is I bought good low-mileage used one for ~$50 shipped.