Oyster,
To see how glutathione fits in with the concept that anything that reduces BBB dysfunction is good news for PD symptoms, you need to do a search to find what effect glutathione has on BBB permeability. Glutathione is well known for its positive effect in improving symptoms, so we would expect it reduces permeability.
I did a quick search and sure enough, found that it does reduce dysfunction of the BBB.

http://www.springerlink.com/content/n6166473240wr556/

"It was also shown that observed BBB permeability dysfunction was associated with brain GSH depletion."

Also see

http://www.meao-cfs.on.ca/about_me/res_bloodbrain.shtml
"Certain deficiencies such as glutathione and essential fatty acids can lead to the barrier becoming more permeable, as can acute and chronic stress."
meaning as your level of glutathione drops, the BBB becomes more permeable.

Ron