Different model number drive as spare replacement?

Hi, I’d need to buy a spare drive simply to keep it as future replacement for an “old” G-Speed Studio XL RAID-6 (48TB tb-2). The old drives currently working in the RAID have an old model number, a model that is now difficult to find in the market (or it’s pricey, and not sure if it’s refurbished…)
Naturally (I thought…) WD now makes new model number drives that can match my old drives, so I could buy a newer (and cheaper) WD as a future spare drive replacement.
Instead G-Tech support answered to me: We would not recommend buying a different model number, as in a RAID array all drives should be of the same model number. A drive with a different model number even though the specifications might seem similar might not be detected in order to rebuild the RAID.
It shocked me because it would mean a great limitation! (And because if now I’d buy a spare drive directly from G-Tech, I’d have no choice about the model number, then surely I would get a different model number drive than my old drives!)
Please, let me know if you have any experience about that.
(In my specific case, my old drives are HUH728060ALE600, and I thought a good spare drive replacement should be the new WD 0B36039.)

An issue update: I’ve found in my emails an old reply from G-Tech support about a very similar question I wrote in Aug. 2018. My question in short was: “I have 2 RAIDs enclosure (Studio XL and Shuttle XL), so if I buy two different model number’s drives as spare parts (different from the drives in the RAIDs, but also different between the two spare drives themselves), can I mount these two different drives in the same RAID?”
The support answer was:
“I have checked both of your device, both are running with Enterprise Class Hard Drives. The provided HGST drives are both 7200RPM Enterprise Class Hard Drives. Therefore, you can use both drives together in the same enclosure. Please only be careful to use drives with same RPM and capacity in RAID configured enclosures.”

The 2 answers (2018 and 2019) appears to be in conflict…
So, which is the truth?

I have an older G speed Q and need to replace one of the drives in the array.
due to flashing amber light on that slot and red light blinking on off beside solid TB blue light.
BUT not sure how the drive should be formatted before I put it in to begin the rebuild.

please advise