Well, it´s obvious that they haven´t done they´re job right at the dealer when replacing the bearings, so, go and complain.
But, having said that, the biggest problem is that the original steering head bearings are ball bearings. Ball bearings are quite sensitive for bigger impacts, as they only have a relatively small capacity of load ability... but they´re cheap...
. Sometimes they last many km, sometimes they don´t, depending on riding stile.
And then, your problem is the warranty. As your bearings are replaced on warranty, you´ll get the same original ball bearings installed.
On my Varadero, I changed the steering head bearings at 60000 km, as it had started to wobble when taking my hands of the bars, an indication that the steering head bearings are worn. I changed them to aftermarked tappered roller bearings, as theese have a bigger capacity of load ability than ball bearings, and therefore last longer. I´ve now done 60000 km more, and I still can take my hands of the bars at 150 km/h and let it run down to idle, without any wobling at all, despite my tyres have done 24000 km and are about to be changed.
The reason why tappered roller bearings are stronger than ball bearings are simple: if you imagine a tennis ball lying on a flat surface, it will only touch with one small point, but, if you imagine a roller, or a cylinder, e.g. a beer can
, lying down on the same flat surface, then it´ll touch the surface with a line according to the lenght of the roller; much more contact that the tennis ball! That means that the tappered roller bearing can obtain much more pressure before deforming than the ball bearing.
Here is a picture of one of my ball bearing rings, which, as said before, was changed at 60000 km:
It´s clearly to se, that there are pressure mark in it, causing the steering mainly to go straight as the balls will try to remain in the marks, causing the bike to wobble when taking the hands of the bars, as you cannot keep the bike in exactly straight position.