Thank goodness, a diving question.

If your regulator is under warranty and, particularly if it's one of the
warranties that pays for parts used in annual service, yes, it should be
serviced again.  If not, hook it to a tank and see how it breathes on the
surface.  If there are any signs of problems, particularly signs of a
tendency to freeflow, have it serviced.  Either way, try to do at least one
dive with it before going on vacation, preferably enough before to allow you
to correct any problems that show up.

Lee

Not necessarily.

If you reg was well cleaned and looked after immediately following the
diving (no salt or other crap left on it) and especially the second stage
was thoroughly washed in fresh water, then as long as it breathes OK you
should not require a re-service.

For peace of mind it would be worth getting it wet, say by a trip to you
local dive club and a half hour in their pool, or even a quick dip in a
local shallow dive spot nearby (if you have one of these).  don't forget to
wash it out after either of these dunks, as the chlorine based bleach in
pool water is worse for regs and all dive gear than salt!

If you have a tank at hand, try out the reg in your bathtub.

If you have any doubts about your reg, get it checked out. Always better to
be safe than sorry.

Ian from http://www.thescubaguide.com