I've just come across a paper by Gasser et al. [1] that covers much the same ground as the previous reference, but the Gasser paper is specific to Parkinson's. It deals with variations in Madopar and its generics. Madopar is made by Roche. Madopar is commonly used in Europe.

Madopar is a formulation of levodopa and benserazide, typically in a ratio of 4:1. It differs from Sinemet in that it uses benserazide as a AADC inhibitor rather than carbidopa.

Source , Mass , Levodopa, Benserazide hydrochloride
----------------------------------------
Tab Roche, 267-283, 95-105, 27.1-29.9
Generic 1, 265, 92.4, 30.9
Generic 2, 284, 98.2, 27.8
Generic 3, 283, 94.4, 26.9
Generic 4, 284, 95.5, 28.8
Values in mg.

Gasser writes:
"Switching back and forth between brand and generic, or even between generics, is a recipe for problems that may cancel out the savings achieved with the cheaper drug."

Reference:

[1] "Pharmaceutical quality of seven generic Levodopa/Benserazide products compared with original MadoparŽ / ProlopaŽ"
Urs E Gasser, Anton Fischer2, Jan P Timmermans and Isabelle Arnet
BMC Pharmacology and Toxicology, April 2013
Pharmaceutical quality of seven generic Levodopa/Benserazide products compared with original Madopar(R) / Prolopa(R) | BMC Pharmacology and Toxicology | Full Text

John