If you are NOT going to apply a veneer to your stucco finish - but want to seal the stucco from the elements, you have 2 options.
3 or 4 layers of EXTERIOR LATEX paint (psst - the eggshell finish looks best) is a better sealer than an organic masonry sealer. And every spring, you can scrub the exterior of your oven and apply a fresh coat of paint - it not only makes your oven look spring-fresh clean, but each coat provides an additional layer of protection.
ORGANIC MASONRY SEALER is great for sealing your oven from snow and rain. While the manufacturer recommends a reapplication every 5 years - I would do it every 2.
NEVER USE a sealer that is not ORGANIC as it may contain chemicals that can be toxic when subjected to heat from your oven.