I have an ageing Citroen Berlingo van as my daily driver. Regularly serviced every 5 years the last time being 4 weeks ago. I had a smell of fumes in the cockpit which turned out to be some sort of breather that was choc a block with gunk and subsequently replaced. The suggestion was that the area the breather resided in could also have created dampness in the workings for the speedo hence it reading 10-20 miles below normal and that with a couple of decent runs it should re-calibrate itself. It hasn't...... Any suggestions?