Have you verified your Uni-WB? Rawnalyze from version 220.127.116.11 displays the WB coefficients on the histogram panel. They should not be farther apart than 5%.
Shot WB coeffs RGGB: (1.0000, 1.0000, 1.0000, 1.0039). The WB setting file was courtesy of Iliah Borg.
Are you aware of the fact, that the baseline exposure for the D300 is MINUS 0.5 EV @ ISO 100? Accordingly, your adjustment should be +0.5 EV.
Yes, the baseline exposures for the LO/HI ISO settings are different. Before I found out about this baseline exposure stuff I shot at LOW -.33 (ISO 160) because the shadows seemed a bit cleaner, but that's because a smaller baseline exposure is used for that setting was lower. Nowadays I just shoot at ISO 200.