A small but seemingly common issue.
The egr pipe had fractured splitting where it joined at the bypass.
To combat this I've now fitted an alternative egr bypass instead.
It gives you plenty of options, like full pipe removal off the manifold and so on, but I've a egr cooler so I fitted the round blank instead.
Solved my problem but after 200k miles a damaged pipe is a small issue.
I always find the egr bypass to make the Diesels smoother, more free review and so on. I've even tried a cleaned out inlet with original working egr and I just can't find the benefit of not fitting a bypass.
My experiences obviously on several 75 Diesels now, manual and auto.