[Martial Arts] Wrench Limb Damage?

[JulianLW]

Quick question. Maybe I've missed this obvious answer somewhere....

Let's say I have ST 15 but I have bought the Wrench Limb technique up to 18. I successfully grapple and Wrench. Do I do 2d+1 crushing (ST 15) or do I do 3d crushing (ST 18)?

I am pretty sure the intent is that I do the ST 15 damage and the Wrench Limb technique doesn't raise my actual ST for the damage roll but only for the contest, but I thought I'd ask others because the more I think about it, both options seem pretty reasonable.

Thanks!