So if the gauge is a 75320-05A, any idea what the part number for the sending unit is?
That part number is an accessory kit for gauge, sending unit, mount hardware and a small harness. It's a complete kit. Should you ever need to replace the sending unit separately it's listed in the kit part breakdown. Part number 72357-04 for all the versions of the in dash oil temp gauge.
Didn't mean to suggest earlier that because the illumination was different the gauge wasn't a good idea. To me it would be worth doing also. It's information that is worth knowing on these air cooled engines and is certainly more valuable than is ambient air temp (that we'd need a guage for that while riding the bike is logic that always escaped me).
The light looks different. In fact noticeably different. I'd still stick the gauge in too.