No your valve cover gaskets, stamped steel with a rubber coating. If you overheat them to bad they will melt.
NIce WJ by the way.

 

Is it a known as a good model?, despite its high consumption rate!
Are they a big fix to change/repair, or is it a simple DIY job?
thanks

 

If your a DIY kind of person there isn't much you won't have a problem fixing yourself. Jeeps are fairly easy to work on so you save a lot of money in labour. The 99 was the first year of the WJ series so they had/ have the normal bugs that would come with it. Fairly reliable, look good on/ off road, they have good gas mileage but not great and unfourtunately there is nothing you can do about that.