We use Ruscoe 12-1 SeamSealer. It is the sealant we have been using for 25 yrs. No leaking corners... some of that has to do with how the corner is made. If the corner is a pre-fab box mitre... it will leak after a couple of years and it is hard to stop. This sealer can be applied when wet, but it takes a little more time.
Hope this helps.