i dont know about amazon.com US

but for ebay, i bought a couple HGST ultrastars many years ago. When 1 of the drives went bad, i tried to get warranty but couldn't. reason? warranty covered under different region 

So before you buy, make sure you can claim warranty malaysia. That is the first thing you need to ask the seller. Let us know cause i also interested 

Another thing to be careful especially when buying from western digital, make sure the HDD is a CMR (NOT SMR).

wd red PLUS or Pro is the CMR, not the plain wd red afaik. so be careful and make sure u carefully check
In malaysia i tested seagate purchased from local shopee for original. 2 methods i tested. Either they come and collect from you (they send a huge truck). OR, you drive to their drop off depot to drop it off there yourself. Got a replacement both times doing that. Last time could call support center, now cannot, instead have to use live chat if you got to ask something about your warranty claim case.

So i would say seagate warranty (for official hdds) are easy and reliable. But if you buy seagate hdd through unofficial channels, seagate will be very dodgy for not wanting to let you claim warranty. e.g. if u buy seagate hdd of shopee, the HDD MAY or MAY not have proper warranty by seagate. So be very very careful who buy from 

for western digital warranty not sure i haven't tried. but for seagate it didn't cost me anything to get the replacement when i requested rma. unless u did the drop off yourself then you have to pay the fuel to drive there to do that 

but your issue is whether if buy from amazon us if can claim warranty malaysia. that i dont know since i never tested that before