If it looks clean and unplayed, go easy on the cleaning. You could do the following to make sure its slide works nicely and is clean enough to make to you feel confident, and no dismantling would be required:

1. Fill a bowl or similar with hot water to a depth of half an inch. Hold the harp mouthpiece-down in the water and work the slide back and forth repeatedly. Remove from water, keeping the harp strictly mouthpiece-down and shake it out thoroughly. Allow to air-dry, mouthpiece-down still, for 24 hours.

2. Wipe the mouthpiece thoroughly with a tissue soaked in isopropyl alcohol. Allow to dry.

Away you go. Chromatic harps should be at body temperature before being played, otherwise you might have problems with sticking valves. If you do have such problems, it's a whole new ball game, and you'll find out why a lot of us tend to steer clear of chroms.

Cheers!