i think wrinx pritty much covere it there.
the 155 is a demon when it comes to havig juddery wipers. you gotta really take the motor unit out and take a look at it... the grease ends up getting in to the contacts, so all you need to do it take the cover off it and clean the grease off the disc/contact arm. That'll usually solve most of yer trouble.
To get to it just take off the black cover below the windscreen (outside if the car) it'll have about 11 torx type screw holding it on... you'll then see the wiper mechanism.. you should be able to undo the retaining bolts for that and take it out of the car. Have a fiddle as described above and fit it back together.
You may still get some slight juddering after that... The 155 fancy wiper arms seem to push down onto the windscreen rather hard (sounds silly i know) and this can and prolly will cause slight juddering problems too... just get some new arms off a 145/6 or a 156 and fit them.. you should be fine after that.
The replacement arms look a bit weedy in comparison to the OE ones though.
I sorted my juddering by replacing the extremely worn mechanism with one I got from Tim Hayes.
There was no grease on the connections of my motor and it had been replaced by the previos owner (probably to try and cure the judder).
My wipers work fine with the OE arms which is why I then sold my conversion kit.