All right, I've removed the textures from tutorialsforblende3d.com, I do not want to give any trouble.
I've added another model, a simple support with a ball bearing, found anywhere in factory setting. It must be unzipped in a models/objects/joint folder.
I've fixed the -check errors. I cannot see any difference in performance or in graphics, but I fixed them anyways.
Fixed the dropships, now they work.
For the motor texture, I've heavily modified some free textures. That texture is an original creation by me, now.
Fixed all the graphical glitches, now the map looks quite different. Thanks for the pointers, this is the sort of feedback I was looking for!