Girard Perregaux 42.1 calibre - stiff handwinding

I have two GP 36,000 bph watches, one with the 32A calibre and the other with the 42.1. I understand that these movements are almost the same, the 42.1 is a later version that adds hacking seconds and one or two other minor tweaks.

My 42.1 has always been extremely stiff to handwind, to the extent that the winding pinion sometimes slips on the crown wheel. I'd assumed that is was just a "feature" of these movements and that the slipping pinion was just down to accelerated tooth wear due to the stiffness. However, now that I've acquired my 32A I notice that it handwinds just fine - stiffer than average perhaps, but not nearly as stiff as the 42.1 and no slipping of the winding pinion.

So why is the 42.1 so stiff, and is it fixable?