Having picked up WFRP 2nd edition again after (quite) a few years, I'm not sure how the off-hand penalty works, if it applies only to attacks or to any and all actions performed with it, including parrying etc.
The Ambidextrous talent (p.97) implies there's a -20% WS/BS penalty for using a weapon in your off hand. It does not say this would affect attacks only.
The Balanced weapon quality (p.105) again implies there's a normal -20% to your WS when wielding a weapon in your off hand. It does not specify attacks only.
The description of Main Gauche, that is, a left-handed dagger (listed on p.108, described on p.109) implies that it was designed for defense (parrying) and not attacking, and it has the abovementioned "Balanced" quality. This in turn implies that parrying with an off-hand weapon not designed for defense carries the -20% penalty.
However, Two Weapon Fighting tells us (p.130) that attacks from a secondary hand suffer a -20% penalty. There's no mention of other actions (including parrying) carrying the same penalty. (This could be because the paragraph focuses on attacking, though.)
I haven't found any other generic statement about a normal penalty to using your off-hand. Maybe I've missed it only, though.
My question is:
When does using your off-hand confer a -20% penalty in WFRP 2nd edition?
Is it just and exclusively for attacks, or for any and all actions including parrying with shields etc (unless there's something like "Ambidextrous" or "Balanced" that offsets it)?