2000 Mercedes E320 electronic ignition switch

I have a 2000 M-B E320 showing increasingly frequent ignition switch failures. The key inserts and turns but there is no response in the “start” position. Repeated turns from “on” to “start” eventually (maybe 10 tries) leads to normal start. No difference if key is totally removed and re-inserted. Both keys have same problem. Sometimes there is no failure, but I can’t link it to ambient or engine temperature or other variables so far. Keys work fine for remote door locks. Dealer is diagnosing but says if keys are not the fault, the next step is replace the EIS (electronic ignition switch) for $1600. Is there any other approach? That seems an extreme price.