Walther LP53 - Help Needed.

We have a few Walther LP53 pistols in our club now, but two of them have a much heavier first stage trigger pressure on them than all the others - making them harder to shoot at 10 meters than the others that have a better trigger feel.

This first stage pressure appears to be controlled by the little hair spring fixed to the trigger blade - but does anyone know if this trigger spring pressure is adjustable in any way?

Maybe Walther made two distinctly different weights of spring to control the trigger weight - a heavy one for firearms practice, and a lighter weight one for air pistol target shooting?

Any help about this would be appreciated so we can change (or adjust) the two LP53 pistols that have the very heavy trigger sping weight on them to make them like the other LP53 pistols that are much easier to use for target shooting.