Well done :) you're right about the weathering, although a good selection of photoshop brushes ( or whatever else you use ) goes a long long way. Not that you need 'em...
I tend to use very off-white for white, quite grey/cream depending how faded or dirty it is; white will do exactly what you say and go washed out. I have no idea why it'd be going transparent, alpha channel for a body texture will be the specular level. I'll go look at the bumpmap now I can get to it.
White lines at the end need a little bump downwards :)
Bumpmap is diffuse3.nm/.nmc, UV mapping should be exactly the same so you can slide it in as a layer in your paint package to get your additions lined up.