Welcome to our forum.
A lot of older tubs did this and there is now a product called geloy that many plastics manuf. are adding to the plastic mixtures to prevent this. It is caused by chemicals and ozone i believe. Maybe Caldera has made some improvements since you bought it
Good Morning - We do hear of this discoloration occasionally. Contact your authorized Caldera dealer and they will provide new levers at no charge to you as this service is warrantable. If you have difficulties in getting the new levers, please use the toll-free number in the back of your owner's manual to contact us at the manufacturing plant. pww
Since this is a reoccuring problem not just with caldera but with a few other manufactures I would be curious as to if you have an ozone if so what size and if it came from caldera. Also what is your chemical routine. This looks like chemical discoloration to me. Chemical or ozone.
Certainly the ozone/chems brought out the issue but seeing the air valve in between and the jet facings all looking fine tells me the plastic on those diverters did not hold up as well.
As i'm sure you are aware, the diverter valve is produced from one vender while the air valve is made by another. The diverter valve is made of a stiffer stronger plastic to prevent it from breaking when the valve becomes harder to turn. It is very common that one type of plastic will change colors while another looks perfect. I would really like to know what chemicals are being used in the tub.