We had 420 that we got used worked good for a while, but developed a fuel issue. I know it had a cracked fuel line that we fixed, but it still didn't run right. Dealer came out and never did get it fixed 100%. Last I knew since I no longer work there was the dealer was taking it back.
There is a local rental company that has switch from linkbelts to Doosan/Terex. There mechanic was telling me they have been having issues with them, but we didn't get into what. Sorry I can't provide more info.