MDI can no longer report no indications of instrument ageing. On 12 March 2000, it seems like something got stuck in a shutter bearing, after a couple of days of slightly increased jitter. Since then, an increased level in the exposure time jitter has been observed. The jitter does not appear to be increasing with time -- rather, it appears to be settling somewhat. However, the shutter needs to be monitored for any further changes.
The jitter causes some noise in the magnetic field measurements (mean field noise of up to 1 gauss), and low frequency modes (l=0-3 p and g modes).