If you had soda in the keg, you will need to change out the rubber parts (which is easy to do -just unscrew the posts, pull the dip tube(s) out, slide off the rubber seals and slide new ones on -of course, give all the SS parts a good thorough cleaning -I use hot water and OxyClean but truly any detergent will work fine. Soda flavors get into the rubber parts.
The only rubber parts I've never changed out were the poppets in the posts -either they don't absorb enough to make a difference, or their surface area is too small to make a difference -but poppets are kind of expen$ive so I've never replaced them except when they wore out (only two so far) to the point that they leaked.