Shoup has poly for the Massey heads.To help with the digging on the left side try leveling the head, or slightly raising it on the left side. A lot of times the feederhouse is slightly twisted down on the left side, and raising the head where it mounts solves the digging problem. I was having trouble with my 20ft 1859 untill I raised the left side one notch( lowered the left hook)made all the difference. Of course your springs must also be properly adjusted. Another thing to check, is the l bracket below the wobble box( the one with the roller chain hooked to the cam like thingy). this bends, and you can't get poper adjustment on the tension spring. Hope I helped Joe