I had wanted to do this climb myself for some time and stumbled upon your report, it was very helpful! I imagine that it is far more challenging in the winter.
As an addendum for those doing it in the summer, here is my summary:
"I hadn't been up the Flume Slide trail in a while. I knew, generally speaking, that the slide extends downwards about 600 vertical feet from the summit. When we had reached 4k and still had not found a decent bushwacking route to the left, I decided we should follow the contour line until we intercepted the rock slide. Needless to say, that was the most nasty bushwack I've ever done. Overlapping craggly branches, rotted out tree trunks covered with moss hiding boulders concealing crevasses..It took about 10 minutes to go 300 feet in the direction of the slide, or so we hoped.
Once we hit the slide the views were absolutely amazing. You have a great view of the ampitheatre between Liberty and Flume. The view upwards is also impressive as there is a noticeable increase in steepness towards the summit cliffs, it must be about 35 degrees on the loose stuff and 60 degrees or so on the summit cliff. We did 2 full length pitches from the 4k level to the base of the summit cliff. This stuff is basically loose talus and scree and very very LOOSE. Rockfall is a pretty decent hazard here, my buddy dislodged a big enough rock that it exploded on its way down and actually emanated the smell of gunpowder. Not only is the scree loose, but the boulders and rocks that are built into the mountain really want to become loosened as well.
Hitting the base of the summit cliff, we realized that this last pitch was going to be pretty darn serious. There was less loose rock, but it was much much steeper(see pictures). I was only able to set one piece of protection on what had to be a 120' cliff. I looked high and low to set more pieces but there were very few cracks in the rock(lessening the rockfall danger but increasing the fall danger...not sure which one I want more).