Be careful with changing the fan. I ordered one of the Gelit Silent 5 fans and installed it, as it should have the same RPM and airflow. It was really quiet but there was almost no airflow. So checked the original one and the Gelit connected to 12V and both had approximately the same RPM, the Gelit was a bit more quiet but had a little less airflow.
The DS1000z seems to have a resistor in series, as the original one has a RPM of around 3000-3500 when installed (don't know the exact RPM anymore), but the Gelit only around 2/3 (2000 RPM). The Gelit draws more current, that would explain the RPM drop.
IF the Rigol has a temperature sensor installed and adjusts the power to the fan the Gelit would be a very good solution. When it gets hot it will have almost the same airflow as the original one. If the Rigol only has a resisor in series, it might get too hot.
Does someone know if the DS1000z has a regulation for teh fan?