My camper was a couple of years old when I bought it. There were only a couple of problem areas and I replaced the sealant in those areas. Over the past 10 years I have mostly just added extra sealant in high risk areas. I would think a thorough inspection would give you an idea of what is needed. I have repeatedly checked every square inch of my camper. I have added additional sealant almost everywhere.
Under ideal circumstances, dicor should last for decades. The bigger issue is usually poor design or poor construction. Joints can flex and open up on a poorly made RV.