During my ownership of a Discovery 3, the mirrors would often adhere; a Land Rover technician recommended applying a silicone lubricant - I utilise WD40 Silicone lubricant (other brands are accessible), and I was cautioned against using standard WD40 on door locks, hinges, etc., as it may exacerbate the issue, since standard WD40 can become exceedingly tacky upon drying.