Hi,
The video shows how to change the valve stem seals without removing the cylinder head. When the cylinder head is installed, no mechanical collet chuck can be used for compressing the valve springs because the underside of the valves is not accessible. The valves will be held in position by compressed air in the cylinder, while the spring is clamped from above with a special pressing tool. In principle, this procedure can be applied on all engines with an overhead camshaft. The video shows the procedure on an Audi GT 5S with 5-cylinder engine.
https://www.youtube.com/watch?v=MNQ25L5PqAE
The video has a German soundtrack, but English subtitles are available on YouTube.
Enjoy it,
Jürgen