1) Hey Khaine, it looks like my vehicle issue might be different from VagabondClown's. With mechanic mastery and grease monkey 3 I can't make any vehicle in the mechanic station, not even a bicycle or minibike. When I have all the components to build a minibike in my inventory and go into the mechanic station the minibike is not greyed out -- it looks like it will let me build one, but on the right hand side of the screen where I would select the number of minibikes to build there is no button to actually do the building. I also can't build the bicycle or minibike at the workbench or advanced workbench. Since mechanic was my third class, followed by civilian, I'm wondering if there's some conflict between classes?
2) And I'm not sure how vehicle mods work, but I can't build any of those either in the mechanic station. They're greyed out.
On a separate note, I finally dipped my toe into the radiated zone for the first time today and I was afraid, very afraid! You... you... demon! End game has now taken on a whole new meaning for me. Well done.