The answers to your questions is that it depends. The more strength/weight/load a BB sees the faster it wears. The more rain/wetness/washings (especially with a pressure spray) the faster they contaminate and the lube degrades. If the frame isn't well prepped or made the bearings can loosen and/or be cockeyed to each other and wear unevenly.

As I said earlier tonight no seal will keep out all water all the time. Some will have a slower penetration but all will weep in time and once in the water won't come out (as there's very little pressure pushing the water out or it wouldn't have gone in much to begin with). Water will carry the dissolved and suspended grit or salts.

Some bearing designs are serviceable by complete disassembly or removal of seals to allow cleaning and relubing. Some aren't.

You need to find out what brand and model of Bb you have then ask more and/or search for servicing instructions. Andy.