I see in Jeronimo's screen shot for the I-153 the same thing that suddenly appeared for me after I just now installed Tyrl's cockpit repaint mod (with some other small changes to a mesh or two.) Namely, that the upper MG handles are seen through the hood and leather padding. I've tried all kinds of .mat file tweaks to see if I could rectify this, to no avail.
I'm not sure why this behavior results; might it involve the order in which certain elements are drawn? In any event, the handles are not fully seen due to being sliced by the reticle mask; the parts ahead of the mask's plane are invisible. If one were to raise by a suitable distance the lower corners of the reticle mask, this clipping would not occur. But then, the handles would of course be seen in their entirety through the hood as well, which would make them even more egregiously prominent.
My quick solution--instead of altering the mesh--involved making fully transparent the texture elements in misc2.tga which are mapped to the handles. These are the two of the three rectangles at the lower right corner of the .tga. Specifically, of the three which abut each other the two relevant ones are the outside ones, the middle one being used for some other item. In the alpha channel I made fully black the former white rectangles, so as to render completely transparent and hence invisible the handles.