I recently restored several VT100 that were extremely yellowed as well as filthy dirty.
I put the plastics in my bathtub and sprayed them heavily with "Krud Kutter", intending only to remove the dirt. To my surprise, much of the yellowing came off too. It didn't return them to their pristine original color but significantly reduced the yellowing as a tea colored runoff pooled in the bottom of the tub. https://www.rustoleum.com/product-catalog/consumer-brands/krud-kutter/cleaners-and-stain-removers/original-krud-kutter I rinsed with clear water and hit them again with a soaking of the Krud Kutter and more "tea" came off. After a third try, no more tea and so I quit. They look really good now and I shined up the brown plastic areas with some "Armor All" which gives it a nice shine. I did four VT100 this way with the same results on all of them. I don't think any of this was harsh to the plastics and so I will use it again on other yellowed stuff. Chris -- Chris Elmquist