Finishing 'Sappy' pine?

[want2b]

Making a couple of replacement bed side rails. Want to etch names, etc in the sides. What I'm worried about is finishing it. Not a wood expert but I feel the wood is 'Southern Pine'. I've had the wood for at least 3 yrs stored in the attic over my shop, got it from a shop closing so I have no idea when it was cut. When I cut & planed it I noticed areas that looked 'sappy'. When I started sanding the first thing I saw was that the paper in my random orbit clogged quickly. I wiped the boards down with lacquer thinner hoping to remove whatever it was but when I went to the next finer grit the results were the same. 65% of the boards are clear/clean wihte pine but the rest has as reddish/pink tint which is where the 'sappy' grain appears.
I can sacrifice sandpaper to get to smothness desired but am worried that whatever I use to stain & finish it will not adhere. Looking for advice form experienced finishers. My thought is to spray with lacquer sealer first and go from there. Have attached a couple of pics.


Thx, Rick H