The GOLF experiment is a resonant scattering spectrophotometer in flight on board the SOHO mission, originally designed to measure the intensity of the solar radiation at 4 selected positions within the sodium doublet (D1 at λ 5896 and D2 at λ 5890 AA). Each position was determined by a modulated magnetic field and a combination of rotating polarizers (see Gabriel et al. 1995, 1997 for a full description of the instrument). Due to occasional malfunctions of the polarizing element that allows to switch between the two wings of the solar profile, it was decided to stop the mechanism in a safety position. Thus, only two monochromatic intensities, Ib+ and Ib- are measured but a duty cycle close to 100 % is achieved. After more than two years of blue wing measurements we show the long term stability of the GOLF experiment and we discuss their impact on the new derived velocity.