valve stem issues
 

I have a 2006 4runner, just bought in May and my first toyota. I go off road on sandy neck which has really soft sand in places and ruts. It's required by the conservation attendants that you reduce air pressure to 18 lbs.. When leaving they have free hoses to reflate. The end of one of my valve stems broke off and the sensor had to be replaced. big bill to replace at dealer. 1. are these stems that brittle, 2. do you have to have these monitors, 3. is there a way around this issue? I was thinking of valve extenders but don't know if that is a good fix. What i"ve been doing is driving home 2+ miles and using my compressor at home to reflate. just looking for some help on this. is toyota service much more expensive than midas or other shops.