I've always thought that MP-10 Optimus's arms are too long, and I don't like how thin the area around the mid-arm swivel looks compared to the stronger look of every other part of the figure. I leave his arms unextended in robot mode, but that's really just a stop-gap solution. It looks like it'd be possible to open up his shoulders and put something in there to lock the arms at only a little bit of extension (for example---only extending until the mid-arm swivel is even with the bottom of the shoulder). Before I open it up and look around, I was just wondering if anyone has done something like that or if a place like Shapeways or something has a little piece that can be put in to lock the arms at only slight extension.
I know there's a 3rd party company making new forearms for MP-10, but I can't remember what they're called. You could probably search for it. But if you just want to keep the stock arms, I may have a suggestion for you. If you open up the shoulder, you will see that there's a spring loaded tab on the forearm that locks into a groove when either extended or retracted (there's a groove in both positions). What you could do is cut a new groove somewhere in the middle so the arm will lock in place mid way like you want. It should be fairly simple, but just be careful when taking apart the shoulder as there are some small pieces that would be easy to lose. Hope that helps.
