PE R420 ESXi host disk firmware upgrade problem

Can anyone advise how to upgrade disk firmware on a PE R420 running ESXi 6.5?
It has disks type WD3001BKHG running firmware version D1S4.
The downloads page indicates the latest version is D1S6 (SAS-Drive_Firmware_WD3HJ_WN64_D1S6_A06.EXE, shown on the downloads page for this type of server if if you select the default Windows 2008 R2 for O/S). 
I've applied firmware updates via the lifecycle controller (e.g. iDRAC, Nic and RAID firmware) from a repository created using Dell Repository Manager which contains the file SAS-Drive_Firmware_WD3HJ_WN64_D1S6_A06.EXE, however this does not upgrade the disk firmware.
If I upload this file via the iDRAC (Update and Rollback function) it displays "The DUP specified is not compatible with the target device."
If I look under downloads for ESXi 6.5 for this server, there isn't a .vib file for this type of disk.