Hi Doug
My 87 300D had similar symptoms to yours. I monkeyed for a while with injectors and this and that but finally had a comp check done. The results were bad!! No2 down to 180psi. At Christmas I pulled the head off and saw a worn, kind of pitted cylinder (No 2). There was evidence of a leaking head gasket and also some evidence of a leaking inlet valve on no. 2 cyl and I am sorry now I didnt get it seen to before bolting it all back down!! Time pressures. Anyway the engine still runs on 5 cyls on startup and then the sixth decides to knock in when she heats up. At least I know what it is!!
Go for the comp check if possible.