I've had my green (Olfa?) mat for over 14 years. I do rotate occasionally so I'm not cutting pieces and blocks in the same spot all the time.
I've never soaked it in the tub....heck! I don't have time to soak ME in the tub! It's starting to show a little age (aren't we all) but it should last many more years.
Someone mentioned flipping the boards over....don't think I ever did that! Maybe I have a new board just waiting to be used!
Nan