I had some bad luck with the stock seals, as far as I know these are viton.
That's what the valves looked like:
Less than 5000miles on the heads, no measureable wear of the guides.
I need seals with a smaller outer diameter for my new springs anyway, so I ordered a set of these teflon seals:
http://www.summitracing.com/parts/HRS-93315/
They really seem to seal "air tight" when installed. When moving the valve up and down you can feel they put a lot more friction on the valve stem than the softer Viton seals.
They also seem to have a nicer fit on the valve guides.
Is there anyone who had good results with the teflon seals? Or should I just get a set of viton seals with a smaller outer diameter...