Some cars are like this, we've just sold out Outlander with its EML on, its been on (except for a few days when i turned the blighter off) for nearly every MOT, reading the Mitsi forum it appears to be the norm for all dealer supplied LPG converted Outlanders, turn it off its back on soon the LPG fires up.

I wouldn't worry about it, just state the truth on the advert or to a potential buyer, they will see from its MOT history that its been on for every MOT, the few people who will worry about it won't be serious buyers anyway, so it might actually save you having to deal with umpteen thousand muppets, you'll have the pleasure of warding off umpteen million scammers anyway.-.;)