Mark and others,
I don't know if this is going to help bring back the white coloring, but regular liquid dishwashing detergent is good for prolonging the plastic composition, of train and other plastic items.
Back in the mid. '70's, my partner and I responded to a factory where a worker had been overcome by fumes, in the work place, which, was prior to the formation of OSHA.
We responded along with an ambulance crew. The ambulance crew medically treated the aided and we took the particulars for an aided report, as our dept. files these reports for statistics.
While, we were there, I noticed a large, long tub with greenish liquid and older plastic telephone casings, in the wash, being readied for reuse.
I asked a foreman what is being done to the casings and he told me about the detergent
rehabilitating the plastic, so as the plastic can become supple again.
I asked him would it be good for plastic train bodies and he said yes.
BUT, I don't know about the newer plastics, as I have not used this technique, as of late!!!!!
Ralph