Failed EGR Functional during smog test. all other tests passed- 1991 560SEL

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From my readings, the cause is probably a clogged EGR Tube. Bench tested EGR valve - turned out good (it holds vacuum and opens port when vacuum is applied)

I then used a speedo cable with drill to clean egr tube towards the intake with a combination of spraying carb cleaner into the tube as well. I did this process 2 times with multiple drilling each time. The speedo cable is about 38 inches and should be long enough to go past the tube and into the intake.

After re-assemby, I tested by applying vacuum into the egr valve. when engine is cold I can see some rough idling but this behaviour disappears once the engine has warmed up to operating temp. What am I missing here? Should I consider some more cleaning cycles? Or is it possible that the clog is at the exhaust side? Or is this the expected behaviour and that the cause of the egr functional failure may be different?