2004 sebring 2.4l 16 v engine 118000 kms on clock

I actually have no idea what oil they used......
What are they likely to have used?
Would you guys advise synthetic over mineral?
I will flush and do my own oil change this time, but I am unsure of
what to use......
I have read that going from mineral to synthetic or visa versa can
cause gasket to swell and leak.......
thoughts??

 

took the car to the local chrysler dealer at the weekend to get the
noise diagnosed......
they first said they could not hear any problem which was not a
suprise as when I went into the shop with the mechanic to help him
find the noise I could not even hear the engine running due to all the
other noise in the shop.....
So I made him sit in the car with me with all the windows shut and the
motor ticking over..... when there was a lull in the noise in the shop
we could both hear it tapping away and he assured me that it was a
noisy injector which he said was common and nothing to worry about.
He actually got me to put my finger on the injector that he thought
was the noisey one and I could feel it tapping.......
Does this sound plausable as the explanation