When asking for technical help at the very least let us know the version of firmware you are running.Cliff's Calibration (Mapping) Guide is a MUST READ: http://www.vemssupport.com/forum/index.php/topic,97.0.html
"They are quite dirty when I take them out"Fix that problem, and your sensors will last..
On N/A cars lsu 4.2 last 50-70kkm. On turbo(low boost<2bar) without LC also long 30kkm.On high boost, LC , wot ... 1-10kkm , depending on lot of things.