Water – Options to refinish deck

I disagree with @Mike - I don't think sealing it will have much effect on the stain. Two reasons:

1. Deck stains are typically (I'm tempted to say always) pigment stains rather than dye stains. Those deposit pigment on the surface of the wood and penetration is minimal. A sealant shouldn't interfere with that.
2. A sealant will typically be a penetrating sealant not a film sealant, so it shouldn't interfere at all with the adherence of the later stain.

That said, I'm not sure you'll see much benefit from the sealant. Penetrating sealants will certainly give you a bit more time to clean up a spill but they won't prevent a stain: that's why tabletops are usually finished with a film finish, and if they're not, you use coasters and place mats. You wouldn't want to use a film finish to a deck because it will certainly peel in short order as the wood expands and contracts under rain and sunshine.

I wouldn't bother. If food gets spilled and you're worried, scrub right away with soap and water. I'll wager you won't notice any minor food marks after the stain has been applied.

Sorry to be the bearer of bad news, but there is no magic solution you can spray on and restore the original beauty. As an owner or an older Carver with lots of teak, the only solution is to sand it down. We solved the every year restoral ritual by using Seatrol medium sealer by Sikens. (found in marine stores) Couple of coats of this stuff and your teak will look good for years.