Fan with part# WG2CK is compatible with R720xd platform. For R720 platform we need to use FAN with part# WCRWR, 3RKJC, WPVP9 or KVN8J. I am not sure about RM4HX. Can you share a picture of part with Dell P/N RM4HX-A00.
I have a sled of SanAce fans that have Dell P/N RM4HX-A00 -- I'm hoping they are compatible with an R720, however I saw some references that associated them with 11th generation servers.  Would these be officially compatible with an R720?   I'm not certain where to find definitive Dell part number information, it isn't listed in the manual.  If there is a definitive source I could be checking please do let me know.  I would hate to bother the forum for something I could be looking up myself.
Fan part number identification (compatible with R720?)