I had posted a GTG with this 1883 MS 64PL a few weeks ago. The slab was filthy, and encrusted, with many scratches, but I really liked the coin. I said I would repost it, before and after. My curation was first, using a shark hand steamer on the slab, to get rid of dirt. Then, I rubbed it down with alcohol. Last, I used auto polish on the slab, and buffed it. Results? Judge for yourself. BEFORE: AFTER:
You're lucky. NEVER use alcohol on plastic! It will damage or actually dissolve some types of plastics or leave a white residue behind that WILL NEVER COME OFF.
I think you are thinking of acetone. Alcohol won't hurt the plastic. I use it all the time to remove residue from pricing stickers.
One day, I slowed down for one of those "high school kid" car washes. They took one look, shook their heads and motioned for me to keep going.