From what I know and experienced, there are only one or two camera service centre in SG which uses the dismantle and cleaning method. More expensive, longer time (few days), but more care, clean, and lots of efforts.
As for other service centres, they usually only use spray or swab from outside methods which anyone can do it themselves. More affordable, very much less waiting time (sometime even almost on the spot), but really need to double check.
IMO, try to clean it yourself regularly unless it is too dirty.