How badly is it leaking? A few drips from the valve cover gasket is not anything to be concerned about. On the other hand if it's making a real mess you'll want to replace the gasket.

You mention “service” so I presume this was at a dealership?  Either way, did you confirm with your own eyes afterwards that there is a leak at the valve cover?  

I am with DayWalker on this.  You said "report."  Who did the "report?"  Have you confirmed the problem yourself, if it actually exists?  Dealer will sometimes squirt some oil under shock absorbers or next to valve covers and try to convince you that you need expensive, although unnecessary work.

When you pick it up, ask them to "show you". Weaping is nothing and many service dealers will want service work. If car shows dripping/leaking and maybe even burning it on the hot engine, then it needs to be replaced.

1. Wash down the valve cover area with something that cuts oil like Dawn dish detergeant.

2. Dry it thoroghly

3. drive it for a week and check the area with a bright light.

4. If the leak is minor then it is a "seep" and not to worry. Anything more, replace the gasket.

The service was done by an independent mechanic. Anyway after reading the comments , I remove the "beauty cover" and saw no oils on the foam or on the cover. Then after I washed the engine bay using degreaser and water. All oil build up on the engine gone....:)

I will keep on eye on the engine. I feel it is all dry no leaking or anything...

Also the report say I need to replace the serpentine belt as well ( mechanic recommend replacing this every 100,000km). What you guys think?

I feel like I need to start doing this kind of small repairs by myself.

The belt needs to be replaced if it has disintegrated or as per the manufacturer's maintenance schedule in your owner's manual.