LUCAS - if you mean the really wide flat head slotted screws that are flush with the outside of the housing, those hold the magnets into the casing. Don't remove those!
To get to the brushes, you remove the two l-o-n-g tie bolts then gently tap the end cap on the pulley end off the steel housing which removes the armature, then tap the other end cap off the housing. The brushes are in spring loaded holders about where the two connections are on the back end of the housing.
For re-assembly, the housing slides over the armature, there's alignment pins to make sure it's lined up correctly, then you hold the brushes back and slide the armature the last inch or so in place, then install the back cover, install both l-o-n-g tie bolts. and DONE!
Been a while since I had one apart. As long as you don't have to replace a bushing, bearing, or one of the terminals & insulator bushings they are not hard to work on, just dirty with all the carbon dust. You should use Brake-Kleen to clean the commutator, the part of the armature the brushes ride on. Starter/generator shops normally recondition the ommutator by turning it on a lathe to make sure it's round, then under-cutting the mica, the insulating material between the segments of the comm, but that takes special tools.
If you look in the local big city phone book tere may be another starter/generator shop around.