Help needed to solve white smoke from '05 LDV Maxus?

I took my van to an LDV specialist who did a compression test on injectors, which were fine. They then checked the EGR valve and said diaphragm was seized and promptly replaced it. The van still smokes. I have also put in a coolant additive, which seals cracks and leaks but no change. Has anyone else had this problem who could offer advice, please?