Just read your first post, glad you're both OK. Sounds like a similar situation I had last year, just started to sprinkle on a well worn (shiny spots) tar and chip road. I was 2 miles from home going slow (20 mph) because I knew it hadn't rained in a week, and was wet enough to be greasy in the corners. I came to a stop sign, left slowly up a small grade for 100 feet or so, and at the top, rear wheel spins on some kind of grease. Zig zagged a couple of times and I couldn't hold it. It threw me (gently) high side, and both bike and I slid for 100 feet on damp pavement slightly downhill. Cosmetic damage to one side of the Goldwing, but expensive. No traffic on a narrow road, and missed a strip of guard rail cables. The guy who stopped to help me pick up the bike said they were doing a big driveway paving job down the road, and on the top of the hill was where all the trucks were turning around in a driveway. Sure enough, when I checked, it was greasy up there. My jacket had a couple of small holes where I did a skydive belly slide, all other gear was OK, minor scuffs, no real damage. I did manage to sprain my rotator cuff, which took months to heal.
Long story, but, I know about unexpected grease. Yours was waaaaaaay worse than mine, but I'm feeling your pain. I hope you can recover all your losses on this one.