Thanks.
I painted the booard section and skull pits to taste (adding a layer of black in the cracks at the end), and sealed everything to make sure the paint/washes would stay in place. Then, I added the green in relatively thin layers, mixing in a brown splotches between the layers to add some pond scum to the radioactive ooze.
The green is Woodland Scenics Realistic Water + Vallejo Model Color Transparent Green. The mix is a whole lot of Realistic Water to one drop of green, well stirred and applied liberally with a spoon. I used the spoon to drag some of the green out into the black cracks.
The brown splotches are Realistic Water + P3 Battlefield Brown, mixed up the same way but applied only to specific spots that seemed appealing to me.
When it was all dried, I painted gloss sealer over the green to bring out the shine and prevent scratches.
Next time, I might use even less pigmentation. I think it turned out a touch opaque for the radioactive ooze effect I was going for.
However, it has set me thinking on new methods of painting drool, blood, ooze, slime, etc. I have some RT Nurgle Marines that might benefit from this kind of effect.