i found that the driver side wiper has some free play, about 2-3 degree. at first i suspect it's the motor however the passenger side is very firm. and after viewing a few diagrams and this youtube video
Subaru WRX windshield wiper mechanism [HD] - YouTube
i suspect it is the mechanism/linkage of the driver side got something that is lose. i must inspect it before going to buy parts.
what do u guys think it could be the problem?
on top of that, i try to remove my 'Cowl panel' so i can get to the motor, base on web info that i pop out the big rubber seal, which was held down with a few clips at the bottom of the panel. however there is no plastic rivets that holds the cowl panel down. on that youtube video u can see there are metal bits of body extend down with a hole on it i would think it's for mounting the cowl panel. but on my car it has no bolts. any ideas ??
my car look like this, it's a right hand drive
https://skydrive.live.com/redir?resi...BF90A69D%21922

I had a similar issue with my GC8 that I detailed in this thread...

http://www.perth-wrx.com/vb/mechanic...r-fix-gc8.html

Had a lot more play than you seem to be describing but it's probably one of the bushings in the linkages that's worn.