Thanx for all the interest you are showing. Will try to give my views on all the points you mentioned in your message.

1. Im a sane rider. I do not accelerate or brake rapidly. I build up speed only when i know that i have suffecient length of road.
2. As i wrote, i have been using valvoline mineral oil. I believe its certainly not the best in the market but isnt bad either.
3. I trust the mechanic but as far as his competence is concerned, I really am no judge as i myself dont have any practical knowledge about bikes and repairs. I certainly hope that he is good. Havent had any other problems till now.
4. clueless.
5. clueless again. any symptoms to diagnose this?
6. wouldnt know. would be thankful if you can tell me how i can find this out.
7. Again no clue.

At the risk of sounding like a moron, i do admit that i do not have much technical knowledge as i have learnt biking very recently (an year back. thanx to xbhp).
I dont have the chains, never thought i might need them.

well timing chain works for long. just like what raccon said in his post. provided the riding is sober. IF the riding is bad then it can go in 3 year. this is what happend to my HHCD100SS/93 model. So I changed it once but later my bike is still with same timing chain. So UR issue is bit annoying me. Well i feel either 1. the riding is bad
2. Oil quality is poor.
3. mechanic don't know how to install it.
4 bad quality bearing which is for cam shaft.
5.worn out timing wheel on crank.
6. misaligned cam shaft or crank shaft timing wheel.
7. timing pad is not proper so it might give proper tension on chain which may cause rubbing the chain on block or related metal spare. Can u please take some of the pisc of u r old chains (close range pics)