First a lens weather sealing alone would not be good if the camera is not WR. I assume that you use a K-7/K-5.
On the other hand, I have used many lenses in foul weather incl. sub-tropical rain. So far so good, but ... It is important to stress that WR does not mean water proof. In hard rain, I woud still wipe regularly the lens (+ body), protect it with a raincoat or better a rain sleeve.
Light rain is not an issue: a wipe from time to time and a light cover is OK. The rain sleeve is usefyl on the other hand for hard rain.
When I do bushwalking, I like to wear a poncho-like raincoat. I can easily keep my camera+lens under the poncho, and access it rapidly when needed. I have also a wipe nearby. (I add that none of my lenses are WR, but I have a couple of very sturdy lenses. I like to shoot in fould weather and this was my motivation to get the K-7. No regret to date.)
Lastly I must mention lens-swapping. This is a no-no under the rain. I prefer not to take any risk, and I avoid any form of lens swapping under the rain, unless under cover and in a dry place.
Hope that the comment will help.