Front wheel Fork is having scratches and Oil is getting leaked from it? I thought that it might be a fault of Oil seal but Mechanic was telling that I have to replace both the fork If I replace only the Oil &amp; Oil seal then again It will leak oil.

Is it a dangerous problem and should I replace both the forks?

Below is an image found on this blog
http://thegoldenwrench.blogspot.in/2012/04/same-sad-story.html

Thanks.
That stanchion is stuffed and needs to be replaced.  If the damage is from normal wear and tear the other will need replacement - probably cheaper to get a whole new fork. If its accident damage (e.g from rubbing while on a car rack) and the other is in very good condition, replacing the damaged one is an option (if you can find a single replacement). 

Replacing the oil will buy you a couple of rides and a mess to clean up at the end of each one, and the shock will not perform particularly well.  

Its not really a dangerous problem, but the fork will not be working properly and will sag under load.