Might there be an added boot controller between the pressure signal and the wastegate actuator? Maybe one of those ball and spring deals?

Glow light behavior sounds like one or more glow plugs is bad. Check continuity to ground for all glow plugs. Shortcut is to test at the big connector at the glow relay. The connector pins are numbered according to cylinder number. Anything more than 1-ohm is toast. Or cut to the chase and replace them all. Do the records show when they were last replaced?

Sixto
98 E320s sedan and wagon
02 C320 wagon