1990 Yamaha xt600, lot of start up smoke

I have a 1990 yamaha xt600 I bought and it started to smoke really bad on cold start ups after it's been sitting overnight. Once it burns the oil off it runs clean and doesn't smoke at all. I initially thought it was the valve seals but I am hearing of a lot of people having this issue and after a rebuild it still does it so with only 7000 miles on the bike, I am thinking it's something else. It really took a turn for the worse quickly so something went wrong. I have heard there is an oil valve in the right hand cover that stops the flow of oil like a one way check valve but I don't know enough about these engines to really get a feel for it. I do know checking the oil seems to be a PITA as I run the bike, let it idle, check and it won't even be on the dip stick, idle some more let it sit for a minute, then there's too much. So I'm wondering if that has anything to do with the oil burning.

Here is a video of a cold start. Notice it runs clean for a bit then the smoke comes on, I would think if the valve seals were gone it would smoke right away and probably not last as long. It will smoke for 2-3 minutes while warming up. Again it just started this and only has 7k miles. Any experience with these that you could share would be great.

http://www.youtube.com/v/JGtAQLGjsPM

yeah that was my first thought too.. I'm being told the only way to change them is to pull the whole motor and remove the head. I was hoping you could pressurize the cylinder to hold the valves up, then remove the locks and springs from the top side so I didn't have to tear it all down.