Most antennas are sealed "good enough" for typical/"normal" use. If you live in sort of 'worse' weather conditions then I'd certainly think about it. Sealing an antenna in the desert is not as probable as in a tropical environment. Can sealing an antenna be detrimental? Yes, it can be. Not very likely, but certainly possible. How do you tell if you should or not? Experience is the 'best' teacher'! Also the hardest.
like these antennas,they have a drain hole,but seal connections no need to let water in.besides ive seen drain holes freeze but above where it couples still let water in. Drain hole is best to expell condensation
So far so good,ive made farther range contacs to repeaters i could just hear,talked simplex farther too.
I suppose its like this. Some buy an item and its bad from the get go,others buy same item its good from get go.
If it works fine a year later im satisfied.
Your milage might vary from mine.
1 thing where i live is about highest elevation in a 50 mile radius .next spring im rasing my antenna from 15 ft to 30 ft. But for now all is well