My MP-15 and 16 sets came today. They're pretty neat, no major issues though the the yellow paint applications on Buzzsaw's body are a pretty sloppy and the spy camera is crooked, though still opens fine.
The pile drivers are specific to each arm. I haven't been able to find any sort of indicative marking but if you flip open the top, the plastic guide jutting out into the cavity should be towards the back.
Viewed from the top:
When you get it right, the pile drivers should click on. Mine do, at least. :)Code:Right arm Left arm
___ back ___
/ | \ / | \
| === Robot === |
\___/ \___/
front