I have a T25 1.9 dg 1983, it's been running well but noticed the tappets seemed noisy so decided to adjust them at the weekend.
As usual nothing on these vans is as straight forward as planned, got to the last set and noticed some movement on the rocker. So I had been loosening off the 15mm nut, turning the adjuster with a screwdriver until it just made contact with the push rod and then adjusting 2 full turns and then locking off.
However the last one on the passenger side, closest to rear bumper is not held shut, so when you press the rocker to check it's tight before adjusting 2 turns, it can move freely so you can't tell how much to adjust it. If you rotate the engine, it will move open when it should but it just doesn't have any pressure holding it the rest of the time. It's a little hard to explain so I've shown a link of a video on google to hopefully show it better.
I'm wondering if a hydraulic tappet is no longer holding pressure and that's why I can push the rocker back down when the valve is shut?
Any ideas would be appreciated thank you

https://photos.app.goo.gl/tFwxnMSr4JNpTHEM8
There's a video of the engine running aswell, they never seem to sound smooth on a video but don't know if mine is good/bad. The smoke is just a small bit of oil that leaked when I took the rocker cover off