The Webasto Air Top 5000 D Blower Motor is now obsolete and no longer available to order from Webasto. This heater version, as well as the 5000 ST and EVO 5500, has now been replaced by the Webasto Air Top EVO 55 12v Webasto Air Top EVO 55 Diesel Heater 12v 4111389A | 9028025B | Butler Technik.
To upgrade to the new heater version you will need to replace the Heater Unit, Fuel Dosing Pump and Wiring Harness. The rotary rheostat controller can still be used with this heater version, though digital controller options like the Webasto Multi Control or the Smart Control are available.
I hope that this information is helpful.