This paper is a bit hard to digest, but it reminded me of the whole idea of "oxidative damage" of molecules that can be oxidized to form highly reactive intermediates. There has been (as you know) a lot of investigation of why the nigral neurons are dark in coloration. It's because thhey are pigmented by melanin. An intermediate in the polymerization reactions to form melanin is 5,6-Dihydroxyindole, or 5,6-dihydroxyindole -2- carboxylic acid. These molecules are formed from dopamine or dopa by catalytic oxidation reactions. Now the 5,6- dihydroxy part of the molecule is really an "ortho quinone" which is the reactive precursor to melanin formation. Just one little paper of a search on "5,6-dihydroxyindole toxicity" reveals that this molecule in itself is cytotoxic and biochemistry around it may be responsible for cellular damage of dopamine producing cells. The whole idea relates to what you have posted because "dopamine is easily oxidized and must be protected from the rest of the cellular organelles". Thus, it seems that dopamine must be "packaged by heavy duty vesicles" or it leaks out and causes dirty things to happen.
http://www.ncbi.nlm.nih.gov/entrez/q...&dopt=Citation

Is just one paper that outlines the research and thinking along these lines. ONe can do a lot of searching to find good work that may illuminate what is going on in dopamine producing cells. There is an answer yet to all the speculations of the etiology of PD in the research community. I think they are barking up a possible tree of the "how" of PD on this one. There is much chemisry going on that we have hits but no cigar as of yet. cs