EGR Leak (Smoke test)

I recently bought a smoke machine for our workshop and have noticed smoke coming from the EGR valve during smoke tests on multiple cars (7-8 vehicles) with over 80,000 km mileage.This smoke coming out from an EGR valve isnt' normal? . I'm wondering if there's a way to test for EGR leaks by removing from engine bay.I own a Toyota Vitz 1.0L and have replaced the EGR leaked valve with used one, but it started giving smoke after couple of days again, though after replacing it resolved my long crank issue in warm engine & definitely improvement in drive & acceleration.We replaced the EGR valve on a Daihatsu Mira 660cc. Initially, it was emitting smoke, but after taking it for a drive and running it at high RPMs, the smoke cleared up.Update: After doing some research, it appears there's no clear consensus on this issue. Some sources say that smoke shouldn't occur, while others consider it normal. A few people suggested checking for smoke leaks by turning the ignition on and inspecting the system.

It is quite normal, in my experience, to see some amount of smoke escape the EGR valve on just about anything I've ever put the smoke machine on.
I admit that before I knew this, I changed at least one EGR valve that probably didn't need to be changed.

We perform smoke tests through the brake booster for intake leaks, and this EGR smoke issue comes up most of the time.We replaced a couple of EGR valves, which improved the drive and fuel trims on both cars that were experiencing up to a 20% lean condition. Today, we encountered another vehicle with a lean condition—a 2017 Honda Civic. It had leaks from the injector O-rings and the EGR valve. After replacing only the injector O-rings, the fuel trim was corrected.Someone on a forum suggested using KOEO (Key On, Engine Off) to check for smoke around the EGR, so I’ll try that tomorrow.I also plan to smoke test from the exhaust side, starting at the oxygen sensor, to see if any smoke escapes from the exhaust.