I'm not entirely sure if the RSC at Menara Dion will do an "authenticity check" outright or do they?
Instead, bring the watch in and ask them to look it over and give you a service quote. IINM, there is a notice saying that they will charge about RM200++ if you decide not to proceed with service.
Another not-so-honest method is if the watch is still under a valid 2 year warranty, bring the warranty card along and tell them you suspect the watch is running fast or slow and ask them to check it out. If the watch is not genuine or has been tampered with, you'll be informed or the watch will be confiscated.
Best to have the seller along with you so you don't end getting blamed for any loss.