Just bought a wrx 2002 and my engine management light is on, took it to dealer and they say the tumbler valve is stuck? 4 hours labour!! may need new valve but cant determine if it just maybe needs cleaning? Dilemma is do i get rid of car or do i find a cheap tumbler valve?

Any help would be appreciated? Prepared to sell if its going to cost me a thousand?
Help anyone can i damage engine and car if i drive with light on and is it safe?
Just seems odd on tickover, drives mint!